Notebook

Operator Overloading¶

Enables class to intercept normal Pytonh operations
Makes class instances act more like built-in types

When Should Operator Overloading Be Used¶

When a class naturally matches, or needs to emulate, a built-in type's interface

Performance¶

Don't expect speed adavtange
In fact, it might be slower. (Might due to the overhead of a function call)

In [3]:

import timeit

min(timeit.repeat("L = list(range(100)); x = L.__len__()", number=10000, repeat=3))

Out[3]:

0.042683540488979155

In [4]:

min(timeit.repeat("L = list(range(100)); x = len(L)", number=10000, repeat=3))

Out[4]:

0.03931401884886343

Command Used Operator¶

__init__
__repr, __str__
__call__
__getattr__
__setattr__
__getitem__
__setitem__                           
__len__
__bool__
__lt__, __gt__, __le__, __ge__, __eq__, __ne__
__iter__, __next__
__contains__
__index__

Indexing and Slicing: `getitem`, `setitem`¶

`getitem`¶

For instance-indexing operation. (e.g. X[i])

In [5]:

class Indexer(object):
    data = [5, 6, 7, 8, 9]

    def __getitem__(self, index):
        print("getitem: ", index)
        return self.data[index]


x = Indexer()
x[2]

getitem:  2

Out[5]:

In [6]:

x[2:4]

getitem:  slice(2, 4, None)

Out[6]:

[7, 8]

Handle the slice object (slice objects have attribute start, stop and step)

In [7]:

class Indexer(object):
    data = [5, 6, 7, 8, 9]

    def __getitem__(self, index):
        if isinstance(index, int):
            print("indexing", index)
        else:
            print("slicing", index.start, index.stop, index.step)
        return self.data[index]


x = Indexer()
x[2:4]

slicing 2 4 None

Out[7]:

[7, 8]

Code One, Get a Bunch Free: `getitem`¶

In absence of more-specific methods, __getitem__ may be used in the following cases.

iteration
in
list comprehensions
map
list and tuple assignment
type constructors

In [8]:

class StepIndexer(object):
    def __getitem__(self, i):
        return self.data[i]


x = StepIndexer()
x.data = "1234"

In [9]:

# iteration

for i in x:
    print(i)

In [10]:

# in

"1" in x

Out[10]:

True

In [11]:

# list comprehensions

[i for i in x]

Out[11]:

['1', '2', '3', '4']

In [12]:

# map

list(map(lambda x: int(x) * 2, x))

Out[12]:

[2, 4, 6, 8]

In [13]:

# tuple assignment

(a, b, c, d) = x
a, b, d

Out[13]:

('1', '2', '4')

In [14]:

# type constructor

list(x)

Out[14]:

['1', '2', '3', '4']

`setitem`¶

For instance-indexing assignment. (e.g. X[i] = 5)

In [15]:

class IndexSeter(object):
    data = [1, 2, 3, 4]

    def __setitem__(self, index, value):
        self.data[index] = value


x = IndexSeter()
x[2] = 5
x.data

Out[15]:

[1, 2, 5, 4]

Slicing and Indexing in Python2¶

In Python 2 only, there are also __getslice__ and __setslice__
They're removed in Python3. Thus, even in Python2, __getitem__ and __setitem__ should be used

Python3's `index` is not indexing !!!¶

Returning an iteger value for an instance and is used by built-ins that convert to digit strings

In [16]:

class C(object):
    def __index__(self):
        return 255


x = C()
hex(x)

Out[16]:

'0xff'

Iterable Objects: `iter`, `next`¶

Iterations first try __iter__ first than __getitem__
Generally, __iter__ is prefered. It supports general iteration context better than __getitem__
When __iter__ is invoked, it's expected to return an iterator object.
If it's provided, Python calls this iterator object's __next__ until a StopIteration exception
It's designed for iteration, not random indexing.
Thus, if indexing is needed, __getitem__ should still be used.

Single Traversal¶

In [17]:

class Squares(object):
    def __init__(self, start, stop):
        self.value = start - 1
        self.stop = stop

    def __iter__(self):
        return self

    def __next__(self):
        if self.value == self.stop:
            raise StopIteration
        self.value += 1
        return self.value**2


def test_iter():
    x = Squares(1, 5)
    I1 = iter(x)
    I2 = iter(x)

    print("I1: ", next(I1))
    print("I1: ", next(I1))
    print("I1: ", next(I1))
    print("I2: ", next(I2))


test_iter()

I1:  1
I1:  4
I1:  9
I2:  16

Multiple Iterators on One Object¶

Method 1: yield¶

When yield is used, it return s a new generator object and create __iter__ and __next__
- It's still true even if the generator function with a yield happens to be a method named __iter__

In [18]:

class Squares(object):
    def __init__(self, start, stop):
        self.start = start
        self.stop = stop

    def __iter__(self):
        for value in range(self.start, self.stop + 1):
            yield value**2


# Defined above
test_iter()

I1:  1
I1:  4
I1:  9
I2:  1

Supplemental class that stores iterator state¶

In [19]:

class Squares(object):
    def __init__(self, start, stop):
        self.start = start
        self.stop = stop

    def __iter__(self):
        return SquaresIter(self.start, self.stop)


class SquaresIter(object):
    def __init__(self, start, stop):
        self.value = start - 1
        self.stop = stop

    def __next__(self):
        if self.value == self.stop:
            raise StopIteration
        self.value += 1
        return self.value**2


# Defined above
test_iter()

I1:  1
I1:  4
I1:  9
I2:  1

Membership: `contains`, `iter`, `getitem`¶

__contains__ is called when in mebership operator is used
- It should be used in membership optimization as special case. In other cases, using __iter__ or __geitem__ is enough
__contains__ should define membership as applying to keys for a mapping and as a search for sequences

In [20]:

class C(object):
    data = [1, 2, 3, 4]

    def __contains__(self, x):
        return x in self.data


x = C()
1 in x

Out[20]:

True

Attribute Access: `getattr` and `setattr`¶

They are used when object.attribute presents

Attribtue Reference `getattr`¶

It's called whenever you try to qualify an instance with an undefined attribute name. (e.g. object.attribute)
It's not called if Python can find the attibute from its inheritance tree
Usage
- Delegate calls to embedded objects from a proxy controller object
- Adapt classes to an interface or accessors for data attributes after the fact - logic in a method that validates or computes an attibute after it's already being used with simple dot notation

In [21]:

class Empty(object):
    def __getattr__(self, attrname):
        if attrname == "age":
            return 40
        else:
            raise AttributeError(attrname)


x = Empty()
x.age

Out[21]:

In Python2 default classes, operator overloading methods run by built-in operations are routed through generic attribute interception methods like __getattr__
In Python3, look up method invoked impliciityly by built-in operations in classes and skip the normal instance lookup entirely
(e.g. printing does not trigger __getattr__ (or __getatttribute__) and a default display is used instead)

Attribute Assignment and Deletion: `setattr`¶

Intercepts *all* attribute assignmet
If this method is defined or inherited, seflf.attr = value becomes self.__setattr__('attr', value)

Loop issue¶

Assigning to any self attriibtues calls __setattr__. Even if it's in __setattr__
To avoid loops, use attribute dict, self.__dict__['name'] = x or by routing any attribute assignments to a higher superclass

In [22]:

class Accesscontrol(object):
    def __setattr__(self, attr, value):
        if attr == "age":
            self.__dict__[attr] = value + 10
        else:
            raise AttributeError(attr + " not allowed")


x = Accesscontrol()
x.age = 50
x.age

Out[22]:

In [23]:

x.name = "Bob"

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-23-6dddaa83334c> in <module>()
----> 1 x.name = 'Bob'

<ipython-input-22-08a9966a8fa9> in __setattr__(self, attr, value)
      4             self.__dict__[attr] = value + 10
      5         else:
----> 6             raise AttributeError(attr + ' not allowed')
      7 
      8 x = Accesscontrol()

AttributeError: name not allowed

Other Attribute Management Tools¶

__delattr__: Used when del object.attr present. (Must avoid recursive loops as __setattr__)
__getattribute__: Intercepts *all* attribute fetches, not just those that are undefined. This would need to avoid loop
Descriptors provide a protocol for associating __get__ and __set__ methods of a class with accesses to a specific class attribute

String Representation: `repr`, `str`¶

`repr` vs `str`¶

__str__
- Tried first for print and str
- Should return a user-friendly display
__repr__
- Interactive echoes, repr, nested appearances
- Should return an as-code string that could be used to re-create the object

Usage¶

__repr__ is used everywhere, except by print and str when __str__ is defined.
Both must return strings
Print falls back on __repr__ if no __str__ is defined, but the inverse is not
- Depending on a container's string conversion logic, __str__ might only apply whne objects appear at the top level of a print operation

In [24]:

class Printer(object):
    def __init__(self, val):
        self.val = val

    def __str__(self):
        return str(self.val)


objs = [Printer(2), Printer(3)]
for x in objs:
    print(x)
print(objs)

2
3
[<__main__.Printer object at 0x02C9B970>, <__main__.Printer object at 0x02C9B870>]

In [25]:

class Printer(object):
    def __init__(self, val):
        self.val = val

    def __repr__(self):
        return str(self.val)


objs = [Printer(2), Printer(3)]
for x in objs:
    print(x)
print(objs)

2
3
[2, 3]

Loop in `repr`¶

Displaying the value of a method riggers the __repr__ of the method's class, in order ot display the class

In [3]:

class LoopRepr(object):
    def __init__(self):
        self.data = "loop"

    def __repr__(self):
        print(self)
        return self.data


r = LoopRepr()
print(r)

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-3-84e11e0ed7d4> in <module>()
      8 
      9 r = LoopRepr()
---> 10 print(r)

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

<ipython-input-3-84e11e0ed7d4> in __repr__(self)
      4 
      5     def __repr__(self):
----> 6         print(self)
      7         return self.data
      8 

RuntimeError: maximum recursion depth exceeded while getting the str of an object

Binary Operation (e.g. add, radd, iadd)¶

The following examples are based on addition.
Every binary operator has similar overloading methods that works the same. (e.g. __mul__, __rmul__, __imul__)

Right-Side Addition¶

__add___ do not support right side of the + operator

In [26]:

class Adder(object):
    def __init__(self, value=0):
        self.val = value

    def __add__(self, other):
        return self.val + other


x = Adder(5)

In [27]:

x + 2

Out[27]:

In [28]:

2 + x

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-28-c1dc2303a7c3> in <module>()
----> 1 2 + x

TypeError: unsupported operand type(s) for +: 'int' and 'Adder'

Python calls __radd__ only when the object on the right side of the + is your classs instance, but the object on the left is not and __add__ handles all the other cases.
When instance of different classes appear mixed in an expression, Python prefers the class of the one on the left

The order is reversed in __radd__: self is really on the right of the +, and the other is on the left.

In [29]:

class Adder(object):
    def __init__(self, value=0):
        self.val = value

    def __add__(self, other):
        return self.val + other

    def __radd__(self, other):
        print("radd ", self.val, other)
        return other + self.val


x = Adder(5)
2 + x

radd  5 2

Out[29]:

Reusing `add` in`radd`¶

For truly commutative operations

In [30]:

class Adder(object):
    def __init__(self, val):
        self.val = val

    def __add__(self, other):
        return self.val + other

    __radd__ = __add__


x = Adder(5)
print(x + 2)
print(2 + x)

7
7

In-place addition¶

To implement +=, code __iadd__ or __add__. The latter is used if the former is absent
It allows for more efficient in-place changes to be coded.

In [31]:

class Number(object):
    def __init__(self, val):
        self.val = val

    def __iadd__(self, other):
        self.val += other
        return self


x = Number(5)
x += 1
x.val

Out[31]:

Call Expressions: `call`¶

If defined, Python runs a __call__ for function call expressions applied to your instances, passing along whatever positional or keyword arguments were sent
All the argument-passing modes are supported by the __call__
Useful when interfacing with APIs(i.e. libraries)
Allows us to code objects that conform to an expected function call interface, but also retain state information
- Many consider such classes to be the best way to retain state information in Python

In [32]:

class Callee(object):
    def __call__(self, *pargs, **kargs):
        print("Called: ", pargs, kargs)


c = Callee()
c(1, 2, 3)

Called:  (1, 2, 3) {}

Comparisons (e.g. `lt`, `gt`)¶

No implicit relationships among the comparison operators.
- e.g. both __eq__ and __ne__ should be defined to ensure that both operatos behave correctly

In [33]:

class Comparator(object):
    def __init__(self, val):
        self.val = val

    def __lt__(self, other):
        return self.val < other


x = Comparator(5)

x < 50

Out[33]:

True

In [34]:

x > 50

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-34-cfde3aaa852a> in <module>()
----> 1 x > 50

TypeError: unorderable types: Comparator() > int()

Boolean Tests: `bool`, `len`¶

Boolean test try __bool__ first then __len__(zero or not)
Python3 renamed the Python2 __nonzero__ to __bool__
- Don't misuse the methods in the two version or it will be silently ignored

In [35]:

class Truth(object):
    def __bool__(self):
        return True

    def __len__(self):
        return 1


x = Truth()
if x:
    print("True")

True

Object Destruction: `del`¶

It's destructor but not recommanded to use. Due to the following reason

No need: Python automatically reclaims all memory space
Unpredictable: When an instacne will be reclaimed cannot be easily predicted. Python does not guarantee that destructor will be called for objects that still exist when the interpreter exits

It's often better to code termination activities in an explicityly called method(e.g. shutdown)

Other Operator Overloadings¶

The following methods would be mentioned in future chapters

__enter__, __exit__: used in with statement
__get__, __set__: used in descriptor
__new__: used in metaclasses

Operator Overloading¶

When Should Operator Overloading Be Used¶

Performance¶

Command Used Operator¶

Indexing and Slicing: __getitem__, __setitem__¶

__getitem__¶

Code One, Get a Bunch Free: __getitem__¶

__setitem__¶

Slicing and Indexing in Python2¶

Python3's __index__ is not indexing !!!¶

Iterable Objects: __iter__, __next__¶