if, else, and elif¶

In [1]:

rain = True

if rain is True:
    agenda = 'Stay Home'
    
agenda

Out[1]:

'Stay Home'

In [3]:

def percentage(a, b):
    if b == 0:
        return None
    
    return round(a/b, 2)

In [4]:

percentage(10, 100)

Out[4]:

0.1

In [5]:

percentage(1, 0)

In [19]:

name = 'Adrian'

if name == 'Annie':
    print('Hello Annie!')
else:
    print("I don't know you...")

I don't know you...

In [12]:

if name in {'Adrian', 'Annie'}:
    print('Hey, I know you!')

elif name in {'Agnus', 'Angela'}:
    print("Hi! I thing we've met somewhere...")

elif name in {'Boris', 'Brunhilde'} :
    # don't talk with them
    pass  # pass can be used in code when sintaxis requires some code, but none is needed

else:
    print("I don't think I know you...")

Hey, I know you!

Inline `if` statements¶

In [20]:

name = name or 'Sigizmund'
name

Out[20]:

'Adrian'

In [21]:

name = 0
name = name or 'Sigizmund'
name

Out[21]:

'Sigizmund'

In [23]:

name = 0
name = name if name is not None else 'Sigizmund'
name

Out[23]:

Using `if` in comprehensions¶

In [25]:

characters = [
    {'name': 'Peter', "surname": 'Rabbit'},
    {'name': 'Josephine', 'surname': 'Rabbit'},
    {'name': 'Michael', 'surname': 'McGregor'} 
]

rabbits = [el['name'] for el in characters if el['surname'] == 'Rabbit']
rabbits

Out[25]:

['Peter', 'Josephine']

Loops¶

`For` loop¶

In [26]:

for i in range(3):
    print(i)

0
1
2

In [27]:

for char in 'Jack':
    print(char)

J
a
c
k

In [28]:

person = {
    'name':'Jim',
    'surname':'Hockins'
}

for k, v in person.items():
    print(k, ':', v)

name : Jim
surname : Hockins

Itertools¶

Cycle¶

In [31]:

from itertools import cycle
colors, categories = cycle(('red', 'green', 'blue')), (1, 2, 3, 4, 5)


for cat, color in zip(categories, colors):
    print(cat, color)

1 red
2 green
3 blue
4 red
5 green

Groupby¶

In [32]:

from itertools import groupby

characters = [
    {'name': 'Peter', "surname": 'Rabbit'},
    {'name': 'Josephine', 'surname': 'Rabbit'},
    {'name': 'Michael', 'surname': 'McGregor'} 
]

for group_name, group in groupby(characters, lambda x: x['surname']):
    print(group_name)
    for el in group:
        print('    ', el['name'])

Rabbit
     Peter
     Josephine
McGregor
     Michael

Product¶

In [33]:

from itertools import product
w1, w2, w3, w4 = 'Hello the wonderful world!'.split()  # splits by the whitespace by default

values1 = []
for el1 in w1:
    for el2 in w2:
        for el3 in w3:
            for el4 in w4:
                values1.append(el1 + el2 + el3 + el4)


# OR
values2 = []
for el1, el2, el3, el4 in product(w1, w2, w3, w4):
    values2.append(el1 + el2 + el3 + el4)

values1 == values2

Out[33]:

True

Enumeration¶

In [37]:

# here, 1 defines starting index
for i, (k, v) in enumerate(person.items(), 1):
    print(f'{i}. {k}: {v}')

1. name: Jim
2. surname: Hockins

`While` loop¶

In [38]:

counter = 0
while counter < 5:
    print(counter)
    counter += 1

In [41]:

from random import randint  # built-in random values generator
counter = 0
minimum = 10

while True:
    value = randint(1, 100)
    if value < minimum:
        print('Below minimum!')
        break

    counter +=1

print(f'Value is: {value}, Samples took: {counter}')

Below minimum!
Value is: 3, Samples took: 18

Additional functionality - break and continue¶

In [42]:

for letter in "Data":
    if letter == 't':
        break
    print(letter)

D
a

In [43]:

for letter in "Data":
    if letter == 't':
        continue
    print(letter)

D
a
a

Try/except/finally¶

Exceptions¶

In [49]:

def _check_raise(inst, type_, text=None):
    text = text if text is not None else f'Wrong value: requires {type} format, got {type(inst)}'

    if not isinstance(inst, type_):
        raise ValueError(text)

In [45]:

_check_raise('Hello', str)

In [50]:

_check_raise('Hello', int)

--------------------------------------------------
ValueError       Traceback (most recent call last)
<ipython-input-50-145b6e9f288c> in <module>
----> 1 _check_raise('Hello', int)

<ipython-input-49-b95b042dc54b> in _check_raise(inst, type_, text)
      3 
      4     if not isinstance(inst, type_):
----> 5         raise ValueError(text)

ValueError: Wrong value: requires <class 'type'> format, got <class 'str'>

Try/Finally¶

In [51]:

try:
    result = 1 / 0
finally:
    print('something is wrong!')

something is wrong!

--------------------------------------------------
ZeroDivisionErrorTraceback (most recent call last)
<ipython-input-51-9d5a90f4a7ec> in <module>
      1 try:
----> 2     result = 1 / 0
      3 finally:
      4     print('something is wrong!')

ZeroDivisionError: division by zero

Try/except¶

In [53]:

try:
    result = 1 / 0
except ZeroDivisionError:
    print('something is wrong!')

something is wrong!

In [59]:

import warnings  
# built-in library that helps warning people - similar to exceptions, but won't halt code,
# you can also set up filter for different warning types

def percentage(value, total):
    try:
        return 100*(value / total)

    except ZeroDivisionError:
        warnings.warn('Total cannot be zero!')

    except (TypeError, KeyError) as e:
        # Keyerror here would never occur - just used it for example
        warnings.warn(f'Something with the wrong: {e}')

    except Exception as e:
        raise Exception(value, total, e)

    finally:
        print('Anyhow, this function was executed!')

In [57]:

percentage(10, 0)

Anyhow, this function was executed!

/Users/philippk/anaconda3/envs/py36/lib/python3.6/site-packages/ipykernel_launcher.py:10: UserWarning: Total cannot be zero!
  # Remove the CWD from sys.path while we load stuff.

In [60]:

percentage('Hello', 'world')

Anyhow, this function was executed!

/Users/philippk/anaconda3/envs/py36/lib/python3.6/site-packages/ipykernel_launcher.py:14: UserWarning: Something with the wrong: unsupported operand type(s) for /: 'str' and 'str'

`With` statement¶

In [62]:

with open('./text_file.txt', 'r') as file:
    data = file.read()

print(data)

Hello
World!

In [63]:

try:
    file = open('./text_file.txt', 'r').__enter__()
    data = file.read() 
finally:
    file.__exit__()

In [64]:

data

Out[64]:

'Hello\nWorld!'

In [ ]: