Python course

Chapter 1. Native datatypes

Module usage

• import path
• default attributes of empty module (name, module etc)

Numeric

• boolean, integer, float, and complex
• numeric operations +, -, *, **, /, //
• math.py, sys.maxint

String

• bytes string: encode/decode()
• unicode string
• r"" and f"" forms

List

• mutable, single types elements
• represented as list of pointers
• indexing and slicing

Tuple

• immutable, different types elements
• could be dict key
• (a,b,c) = x

Set and Dict

• Represented as hash table
• keys() return set
• values() and items() return list

Files

• open and "with" statement
• read() - read all content
• "in", readlines() - read all lines

Chapter 2. Comprehensions

List

• list comprehension provides a compact way of mapping a list into another list
• filesystem comprehension example
• map() and filter() functions
• combine a list comprehension with a sequence reduction
• we can perform database-like queries on sequences
• walrus operator allows you to run an expression while simultaneously assigning the output value
• matrix comprehension example
• list comprehension in Python works by loading the entire output list into memory
• it’s often helpful to use a generator instead of a list comprehension in Python

Dict

• dictionary comprehension similar to list comprehension, but it operates with key-value pairs
• swapping the keys and values of a dictionary example (value also must be hashable and unique)

Chapter 3. Functions

Function as object

• function objects has a number of attributes:
  • doc is the function’s documentation string
  • name is the function’s name
  • defaults is a tuple containing default argument values for those arguments that have defaults, or None if no arguments have a default value
  • code is the code object representing the compiled function body
  • globals is a reference to the dictionary that holds the function’s global variables — the global namespace of the module in which the function was defined
  • dict is the namespace supporting arbitrary function attributes
  • closure is None or a tuple of cells that contain bindings for the function’s free variables
  • annotations is a dictionary containing annotations of parameters
  • kwdefaults is a dictionary containing defaults for keyword-only parameters
  • call is a method that allows the function to be called
  • get is a method that returns a bound method object when the function is an instance attribute
• id() function returns an integer representing its identity
• Bytecode of function can be obtained by dis module

Function arguments

• arguments is a tuple
• arguments can be passed by position or by keyword
• arguments can be empty
• you can Guarantee at least one argument by using *args
• arguments can have default values
• default values are evaluated at the point of function definition. That's why you can't use mutable objects (e.g. set) as default values
• use None as default value and check it inside function
• arguments can be packed (while func definition) and unpacked (while calling)
• unpacking arguments as a list or dictionary
• flatten() example
• keyargs() example

Function scope

• module functions are visible to all other functions in the module
  • Local scope: variables defined inside a function
  • Enclosing scope: variables defined inside a function, but used in a nested function
  • Global scope: variables defined outside a function
  • Builtin scope: variables preassigned in the builtin namespace
• you can define function with function
• inner function has access to outer function params. It is called 'closure'
• global variables can be used explicitly by using global keyword
• keyword nonlocal allows you to assign to variables in an outer (but non-global) scope
• you can use dir() function to get list of names in the current local scope
• you can use globals() and locals() functions to get dictionaries of global and local variables

Lambda functions

• lambda functions are single-expression functions that are not necessarily bound to a name
• common syntax: lambda argument_list: expression
• lambda usecases:
  • sort key
  • filter
  • map/reduce
  • decorators
  • closures
  • currying

Chapter 4. Decorators