Python Introduction with some detours¶

xkcd

Python created by Guido von Rossum in early 1990s (later at Google,Dropbox)¶

Language reference: https://docs.python.org/3/index.html ¶

Why Python?¶

Why Python but not Julia or R or some other language or even VBA in Excel?¶

Readability, Glue Language(APIs), From Startups to Google and Facebook, Pipeline¶

Prime numbers in J language used at some finance institutions 1: I. 2= +/ 0= (] |/ ]) i.y

Python is now programming language # 3 in TIOBE language index (as of September 2018)¶

https://www.tiobe.com/tiobe-index/

https://developers.slashdot.org/story/18/09/08/1722213/python-displaces-c-in-tiobe-index-top-3

https://www.anaconda.com/download/

Jupyter Basics¶

Esc-M turns cell into Markdown cell for formatting (https://guides.github.com/pdfs/markdown-cheatsheet-online.pdf)
Esc-Y turns cell into code cell(default)
Ctrl-Enter runs code of cell in place
Alt-Enter runs code for current cell and creates a new cell below
Esc-A creates a new cell above current cell
Esc-B creates a new cell below current cell
Esc-dd deletes current cell

What is Programming?¶

Egg algorithm
Computers are stupid, they only do what they are told to do
If it is stupid but it works, then it is not stupid
Make it work, make it right, make it fast(last two steps often not required in real life)
GIGO principle
Error messages are nothing to be afraid of, usually the message will explain what needs fixing!

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print("Hello World!")

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# Our first comment
# Real Program Comments should generally describe why
# Here  comments will describe extra information not covered or needed for starting out
# REPL(Read,Eval,Print, Loop) 
# Python - Interpreted Language(commands executed as they come)

Most important Python ideas¶

dir(myobject) to find what can be done (most decent text editors/IDEs will offer autocompletion and hints though)
help(myobject) general help
type(myobject) what type it is

: indicates a new indentation level¶

id(object)¶

Return the “identity” of an object.

This is an integer which is guaranteed to be unique and constant for this object during its lifetime. Two objects with non-overlapping lifetimes may have the same id() value.

CPython implementation detail: This is the address of the object in memory.¶

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myname="Valdis"
# Creating our first variable will persist through this workbook once it is run

Strings¶

immutable

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print(myname)
#print is a function that takes at least one argument
# 2.7 and older Python was print without parenthesis

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-5-f8604fe2a0f6> in <module>()
----> 1 print(myname)
      2 #print is a function that takes at least one argument
      3 # 2.7 and older Python was print without parenthesis

NameError: name 'myname' is not defined

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favfood="potatoes"

"f-strings", “formatted string literals”¶

In some other languages also known as string interpolation

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print(f"My name is {myname} and my favorite food is {favfood} ")
# f strings in Python 3.6+ older formatting methods not covered in this course
# https://realpython.com/python-f-strings/

What is a function?¶

A function is a block of organized, reusable code that is used to perform a single, related action.
Single, organized, related always ? :)

DRY - Do not Repeat Yourself principle¶

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system. http://wiki.c2.com/?DontRepeatYourself
Contrast WET - We Enjoy Typing, Write Everything Twice, Waste Everyone's Time

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def printName(name):
    print(f"Maybe my name is: {name}")

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printName("Voldemars")

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#Functions can also return values
def combinedName(name,last):
    return name+" "+last

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fullname=combinedName("Valdis","Saulespurens")

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sometext="It's a string which allows single quotes"
anothertext='This string allows "double quotes" without escaping'
longstring='''This is a multiline string
Seriously long string with many lines
lots of text covered'''

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print(longstring)

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## Some strings might need escaping such as \\, \", \', \t

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## Everything in Python is an Object
## can use id(myobject) to find its identity - place in memory
## each object has a value with a type and can be mutable/immutable

Data types in Python 3.x¶

Integers type(42) int
Floating Point type(3.14) float
Boolean type(True),type(False) bool
String(ordered, immutable char sequence) type("OyCaramba") str
List type([1,2,63,"aha","youcanmixtypeinsidelist", ["even","nest"]]) list
Dictionary(key:value pairs) type({"foo":"bar", "favoriteday":"Friday"}) dict
Tuple - ordered immutable sequence type("sup",7,"dwarves") tup
Set (unordered collection of uniques) ("k","a","r","t","u","p","e","l","i","s")

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# Variables
a = 5 # Integer
b = 5.6 # Float
c = "sometext" # String
print(type(a),type(b),type(c))

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a = "42" # now a is a String
type(a) # notice how without print the output is a bit different

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# Naming conventions
# start with lowercase
# _ between words or camelCase
# style guide: https://www.python.org/dev/peps/pep-0008/

Arithmetic Operators¶

+ - * /¶

**(power)¶

% modulus¶

//(integer division)¶

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5+4*3-(6/2)

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5//2

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4%3

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type(1)

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type(14.0)

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5**33

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11**120 # no maximum anymore

Python Lists¶

Ordered
Mutable(can change individual members!)
Comma separated between brackets [1,3,2,5,6,2]
Can have duplicates
Can be nested

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mylist = list(range(11,21,1)) 
# mylist = [11, 12, 13, 14, 15, 16, 17, 18, 19, 20] would work too but not practical for longer ranges...
print(mylist)

Slice notation¶

somestring[start:end:step]

somelist[start:end:step]

start is at index 0(first element), end is -1 the actual index

Examples below¶

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mylist[0]

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mylist[3:]

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mylist[:-2]

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mylist[::2]

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"Valdis"[2:5]

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myname[-1]

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myname[::-1]

Common list methods.¶

list.append(elem) -- adds a single element to the end of the list. Common error: does not return the new list, just modifies the original.
list.insert(index, elem) -- inserts the element at the given index, shifting elements to the right.
list.extend(list2) adds the elements in list2 to the end of the list. Using + or += on a list is similar to using extend().
list.index(elem) -- searches for the given element from the start of the list and returns its index. Throws a ValueError if the element does not appear (use "in" to check without a ValueError).
list.remove(elem) -- searches for the first instance of the given element and removes it (throws ValueError if not present)
list.sort() -- sorts the list in place (does not return it). (The sorted() function shown later is preferred.)
list.reverse() -- reverses the list in place (does not return it)
list.pop(index)-- removes and returns the element at the given index. Returns the rightmost element if index is omitted (roughly the opposite of append()).

Dictionaries¶

Collection of Key - Value pairs
also known as associative array
unordered
keys unique in one dictionary
storing, extracting

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mydict = {"country":"Latvia"} #Key-Value store, also knows as Hashmaps, Keys must be unique

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mydict["food"]="potatoes"

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mydict["food"]

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mydict["country"]

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mydict.keys()

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mydict.values()

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"potatoes" in mydict.values()

Sets¶

unordered
uniques only
curly braces {3, 6, 7}

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s={3,3,6,1,3,6,7}
print(s)

Tuples¶

ordered
immutable (cannot be changed!)
Can be used as a collection of fields

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mytuple = 6, 4, 9
print(mytuple)

Conditional operators¶

< > <= >= == != and or not¶

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if 5 >= 5:
    print("hello")
if 5 <= 5:
    print("hello")
if 5 == 6:
    print("hello thats magic")
if 5 != 6:
    print("hello thats not magic")

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def printnum(num):
    if num > 10:
        print(f"This number {num} is too unwieldy for me to print")
    else:
        print(f"This {num} is a nice number")

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def isEven(num):
    if num%2 == 0:
        print(f"{num} is even")
    else:
        print(f"{num} is odd")

isEven(3)
isEven(4)

Loops¶

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for x in range(10):
    print(x)

in Python 3.X range returns an iterable(Lazy, values on demand, saves memory on longer iteration)¶

in Python 2.7 range returned a list ! (xrange was the iterator version, not as fully featured as the current range)¶

Full list of differences: http://treyhunner.com/2018/02/python-3-s-range-better-than-python-2-s-xrange/

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for c in "Valdis":
    print(c)

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for k,v in mydict.items():
    print(k,v)

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printnum(3)

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## Splitting a line of text into words
mytext = "A quick brown fox jumped over a sleeping dog"
words = mytext.split()

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print(words)

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## Print first letter of each word
for w in words:
    print(w[0], w[0].isupper(), w.istitle()) ## istitle() checks every word in a string so not good for unsplit strings

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myline="Mr. Sherlock Holmes, who was usually very late in the mornings"

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words=myline.split()

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words

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words[1][0].isupper()

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def processLine(line):
    words = line.split()
    linegood=False
    for word in words:        
        if word[0].isupper():
            print(word, end='\t')
            linegood=True
    if linegood == True:
        print('')

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class MyClass:
    """A simple example class"""
    i = 12345

    def f(self): #this is important! similar to this in other languages object itself
        return f'Hello'
dir(MyClass)

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myc=MyClass()
#?myc
print(myc.i)
print(myc.f())

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class Complex:
    def __init__(self, realpart, imagpart, name):
        self.r = realpart
        self.i = imagpart
        self.name = name
    def calcDistance(self, mult):
        return (self.r**2+self.i**2)**0.5*mult
x = Complex(3.0, -4.5, "Complekss")
print(x.r, x.i)
print(x.calcDistance(5))
print(x.name)
# dir(x)
dir(Complex)

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# TODO List Comprehensions, Dictionary Comperehensions
# Generators
# File IO
# Filter,Map,Apply

# Imports, modules
# Decorators !

Python Resources¶

Learning

Tutorials Begginner to Intermediate¶

https://automatetheboringstuff.com/ - Anything by Al Sweigart is great
http://newcoder.io/tutorials/ - 5 sets of practical tutorials
Think Like a Computer Scientist full tutorial
Non-Programmers Tutorial for Python 3 quite good for wikibooks
Real Python Python Tutorials for all levels
Learn Python 3 the Hard Way controversial author but very exhaustive, some like this approach

More Advanced Python Specific Books¶

Python Cookbook Recipes for specific situations
Effective Python best practices
Fluent Python highly recommended, shows Python's advantages

General Best Practices Books¶

(not Python specific)¶

Code Complete 2 - Fantastic best practices
The Mythical Man-Month - No silver bullet even after 40 years.
The Pragmatic Programmer - More practical advice
Clean Code - more towards agile

Blogs / Personalities / forums¶

Exercises/Challenges¶

http://www.pythonchallenge.com/ - first one is easy but after that...
Advent of Code - yearly programming challenges
https://projecteuler.net/ - gets very mathematical but first problems are great for testing (Prof. Arnicans used to give extra credit for these...)

Questions / Suggestions ?¶

feel free to pull request

Python Introduction with some detours¶

Python created by Guido von Rossum in early 1990s (later at Google,Dropbox)¶

Language reference: https://docs.python.org/3/index.html¶

Why Python?¶

Why Python but not Julia or R or some other language or even VBA in Excel?¶

Readability, Glue Language(APIs), From Startups to Google and Facebook, Pipeline¶

Python is now programming language # 3 in TIOBE language index (as of September 2018)¶

Jupyter Basics¶

What is Programming?¶

Most important Python ideas¶

: indicates a new indentation level¶

id(object)¶

CPython implementation detail: This is the address of the object in memory.¶

Strings¶

"f-strings", “formatted string literals”¶

What is a function?¶

DRY - Do not Repeat Yourself principle¶

Data types in Python 3.x¶

Arithmetic Operators¶

+ - * /¶

**(power)¶

% modulus¶

//(integer division)¶

Python Lists¶

Slice notation¶

Examples below¶

Common list methods.¶

Dictionaries¶

Sets¶

Tuples¶

Conditional operators¶

< > <= >= == != and or not¶

Loops¶

in Python 3.X range returns an iterable(Lazy, values on demand, saves memory on longer iteration)¶

in Python 2.7 range returned a list ! (xrange was the iterator version, not as fully featured as the current range)¶

Python Resources¶

Tutorials Begginner to Intermediate¶

More Advanced Python Specific Books¶

General Best Practices Books¶

(not Python specific)¶

Blogs / Personalities / forums¶

Exercises/Challenges¶

Questions / Suggestions ?¶

Language reference: https://docs.python.org/3/index.html ¶