Basic Grammars

• Indentation Language, "/" to change line (or use(),"")
• comment #
• initializing and assignment (by tuples) and variable scope

• a, b , c = 'hi', 1, 3.0 # comment
  f=g=10 # chained assignment
  def f(x):
      global d # global variable
      e = 4 # local variable 
      print(a)
  

• all variables assigned by reference

  • [[0] * 2 for _ in range(2)] != [[0]*2]*2
    

• support +=, ^=, <<= ...

Operations

• // for integer (floor) divide
• divmod() - get remainders
• is, is not: compare id
• and, or, not: boolean
  • Semantic Sugar

• • [] or [None] # returns [None]
    [] or [1,2] # return [1,2]
    [1,2[] or [3,4] # return [1,2]
    

• % for remainder
• ** for exponential (^)
• <operator>= supported in most cases
• math library
• logical operators: not, and, or
• bitwise operators: >>, <<, ^, &, |, ~

• 1 > 2 > 3 # true
  

Control Structures

• if then elif else
• for loop - for ( *iter(s) in container):
  • break, continue
  • for with else

  • for n in range(2, 10):
        for x in range(2, n):
            if n % x == 0:
                print( n, 'equals', x, '*', n/x)
                break
        else:
            # loop fell through without finding a factor
            print(n, 'is a prime number')
    

  • ternary expression: <true-expr> if true else <false-expr>
• while
• try: except:
• pass : no operation

Environmental Variables

• If __name__ == "main":
  • when the module (py file) is called directly via interpreter, this will be named main
  • if imported elsewhere the variable is different

Constant

• Constant usually defined as module level , named with CAPITAL LETTERS and underscores

Variable Lifetime and Variable Scope

• variable scope and lifetime is from declaration to program end
• scope is covered inside a loop/conditional statement
• global variable
  • _global _keyword
  • can modify mutable global variable in function
  • cannot modify immutable global variable (eg. += ) in a function without "global"
• nonlocal variable
  • nonlocal keyword
  • similar to global, used for outer scope variable

Import Libraries

module and package

• a Module is a file containing Python code
• a package is a hierarchically structured collection of related modules
• \__name___ is a set to the name of the module_
  • the interactive shell has the name "\__main___"_

mycompany
 ├─ web
 │  ├─ __init__.py
 │  ├─ utils.py
 │  └─ www.py
 ├─ __init__.py
 ├─ abc.py
 └─ utils.py

• from <lib> import <func>
• import <lib> (as...) then specify the full name of the operation(<lib>.operation in your code)
• from <lib> import * (import all) - NOT RECOMMENDED will cover your own variables maybe