python_cheat_sheet.md

****# Python Syntax

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OOP

Syntax	Used To...
self.attribute_name	read an attribute inside of a class
self.attribute_name = value_expression	write an attribute inside of a class and assigning a value to it
ExampleClassName()	create an instance of that class (assuming no required args)
name_of_instance = ExampleClassName()	create an instance of that class and stores it in a variable
example_instance.name_of_attribute	read an attribute from an instance
example_instance.attribute_name = new_attribute_value	re-assign the value of attribute on an instance
self.name_of_instance_method	call an instance method INSIDE a definition
name_of_instance.name_of_instance_method()	call an instance method OUTSIDE a definition
super().parent_class_method()	general syntax for super() method
super().__init__(arg1, arg2, etc)	super refers to the parent class, and construtor of the parent class, and pulls those attributes (passed in as arguments) from the parent class and sets them up as attributes in the child class it's being called in

dir() | list all of the methods that a particular class has (helpful for debugging) vars() | makes a dictionary of an object's attributes (helpful for debugging)

Typical OOP-Related Errors

Error	Meaning
NameError: name 'ExampleClassName' is not defined	This suggests that the class named ExampleClassName hasn't been defined before trying to instantiate it
AttributeError: 'ExampleClassName' object has no attribute 'missing_attribute_name'	suggests that we are trying to read an attribute from an instance of this class, but that attribute doesn't have a value
TypeError: __init__() takes 0 positional arguments but 1 was given	This suggests that the constructor doesn't define the first parameter self

Testing Objects

def test_some_example_test_case():
    # Arrange
    # Create an instance of the class
    # and set up any other necessary test variables

    # Act
    # Call the method that we are testing

    # Assert
    # Verify all relevant return values and state changes

Variables and Mutability

Examples of mutation and modification include:

• Appending or removing an item to a list
• Adding or removing a key-value pair to a dictionary

Examples of operations that do not mutate or modify include:

• Adding two numbers, resulting in a third number, such as sum = 1 + 2
• Incrementing a number stored in a variable, like num += 1

Remember that....attempting to change (adding, multiplying, etc) an IMMUTABLE object actually just produces a different object with a different ID

Whereas... MUATBLE objects do not change object IDs when the object is modified or mutated.

Together that means... when you call a function, you pass a reference from the argument to the parameter, so they're both going to refer to the same object in memory. if it's a mutable object, like a list or dictionary, anything you do to the parameter, gets reflected back to the original argument.

Conditional Operators

and

For and, if and only if both sides are truthy, then the entire expression is True. Otherwise, it's False. "Left" refers to what's on the left of the and, "Right" refers to what's on the right of and, and "Result" is what the expression evaluates to.

Left	Right	Result
True	True	True
True	False	False
False	True	False
False	False	False

or

Expressions with an or evaluate to True when at least one side of the or is truthy. (This explains the short-circuiting phenomenon in Python - if the interpreter finds the left side to be truthy, it will not go on to evaluate the right side).

Left	Right	Result
True	True	True
True	False	True
False	True	True
False	False	False

not

When not is in front of a truthy expression, the entire expression becomes False. When not is in front of a falsy expression, the entire expression becomes True.

Operator Precedence

from highest (()) to lowest (lambda), wherein the highest-precedence operator will be evaluated first, and then on down the priorty line.

Note this important ranking: relationship operators > not > and > or

Operator	Meaning
()	Parentheses (grouping)
f(args...)	Function call
x[index:index]	Slicing
x[index]	Subscription
x.attribute	Attribute reference
**	Exponentiation
~x	Bitwise not
+x, -x	Positive, negative
*, /, %	Multiplication, division, remainder
+, -	Addition, subtraction
<<, >>	Bitwise shifts
&	Bitwise AND
^	Bitwise XOR
|	Bitwise OR
in, not in, is, is not, <, <=, >, >=,<>, !=, ==	Relational operators: Comparisons, membership, identity
not x	Boolean NOT
and	Boolean AND
or	Boolean OR
lambda	Lambda expression