A Quickstart Guide for writing code in Python.

quickstart-python.md

Quickstart Guide for Python

A Quickstart Guide for writing code in Python.

"Python is an experiment in how much freedom programmers need. Too much freedom and nobody can read another's code; too little and expressiveness is endangered." - Guido van Rossum

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Table of Contents

• Variables
• #comments
• Built-in Collections (arrays)
• if Statements
• for Loops
• while Loops
• Exception Handling try: ... except:
• Classes & Objects
• Inheritance
• if __name__ == '__main__': guard

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Variables

No need to explicitly specify type of the variables.

name = 'John'  # string
age = 24       # int
score = 95.0   # float

Built-in data types

• Text Type: str
• Numeric Types: int, float, complex
• Sequence Types: list, tuple, range
• Mapping Type: dict
• Set Types: set, frozenset
• Boolean Type: bool
• Binary Types: bytes, bytearray, memoryview

Strings in Python are surrounded by either ', or ", so 'hello' is the same as "hello". Pick one style and stick to it.

Comments in Code

# inline comments

"""Single line docstring"""

"""Multiline docstring
for longer documentation
"""

Built-in Collections

These are sometimes referred to as arrays.

list_numbers = [1, 2, 3, 4, 5]   # declaring a list using brackets
tuple_numbers = (1, 2, 3, 4, 5)  # declaring a tuple using parentheses
set_numbers = {1, 2, 3, 4, 5}    # declaring a set curly brackets
dictionary_romans = {                       # declaring a dictionary
    'M': 1000,
    'D': 500,
    'C': 100,
    'L': 50,
    'X': 10,
    'V': 5,
    'I': 1,
}

dictionary_romans['M']  # accessing dictionary entry

When deciding which collection to use, think about what functionality you need:

Built-in collection	Ordered	Changeable	Allow duplicate values	Comments
List	✅	✅	✅	Items are indexed, the first item has index [0], the second item has index [1] etc.
Tuple	✅	❌	✅	Items are indexed, the first item has index [0], the second item has index [1] etc.
Set	❌	❌	❌	Items can appear in a different order every time you use them, and cannot be referred to by index or key.
Dictionary	✅	✅	❌	Are used to store data values in key:value pairs.

if statements

In an if-elif-else statement only one branch is going to be executed.

if a == b:
    # only one of these is going to be executed
elif a > b:
    # only one of these is going to be executed
else:
    # only one of these is going to be executed

Supported logical conditions:

• Equals: a == b
• Not Equals: a != b
• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b

When comparing a variable to None use is instead of ==.

if value is None:
    # do something

for loops

for e in [1, 2, 3, 4, 5]:  # iterating over a sequence
    print(e)

for c in 'some string':  # iterate through each character in the string
    print(c)

for i in range(10):  # iterating over numbers from 0 (including) to 10 (excluding)
    print(i)

for i in range(start, stop, step):  # iterating through numbers from [start] to [stop] incrementing by [step] every time
    print(i)

while loops

i = 1
while i < 6:  # while loop body gets executed over and over again until the condition holds
    print(i)
    i += 1

Functions

def my_function():
    # do something

Exception Handling

try:
    # try doing something here that might cause the program to break
    1 / 0
except ZeroDivisionError as e:
    # code here is executed only if an exception of type ZeroDivisionError was raised
    print(e)
else:
    # code here is executed only if there were no exceptions raised
    ...
finally:
    # code here gets executed no matter what
    ...

else: and finally: branches are optional.

Classes & Objects

class Point:
    def __init__(self, x, y):  # this method is always executed when the class is being initiated.
        self.x = x  # assign values to object properties
        self.y = y

    def area(self):  # public method
        return self.width * self.length

    def _area(self):  # protected method (single leading underscore)
        ...
    
    def __area(self):  # private method (double leading underscores)
        ...


center = Point(3, 6)  # creating an object of Point class
center.x  # accessing properties
center.y = 5  # setting properties

Inheritance

if __name__ == '__main__': guard

if __name__ == '__main__':
    ...  # code here gets executed only if you run this module as the main program

More on this on StackOverflow

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Inspired by:

• W3Schools Python Tutorial
• The Best of the Best Practices (BOBP) Guide for Python
• Python Anti-Patterns