Jan 21, 2019

Python Local Vs Global

#########################
#   Global Scope Vs Enclosing Scope Vs Local Scope 
#   LEGB rule
#   Local(L): Defined inside function/class
#   Enclosed(E): Defined inside enclosing functions(Nested function concept)
#   Global(G): Defined at the uppermost level
#   Built-in(B): Reserved names in Python builtin modules
#########################

message = 'global'

def enclosing():
    message = 'enclosing'
    def local():
        message = 'local'
    print('enclosing message: ', message)   # enclosing
    local()
    print('enclosing message: ', message)   # enclosing


def enclosing_nonlocal():
    message = 'enclosing'
    def local():
        nonlocal message    # This refers to the above message in enclosing scope, not in global scope
        message = 'local'
    print('enclosing message: ', message)   # enclosing
    local()
    print('enclosing message: ', message)   local


def enclosing_global():
    message = 'enclosing'
    def local():
        global message
        message = 'local'  # Here you are updating message in global scope, not in enclosing scope
    print('enclosing message: ', message)   enclosing
    local()
    print('enclosing message: ', message)    enclosing 


if __name__ == '__main__':
    print('------------------------------------')
    print('global message: ', message)
    enclosing()
    print('global message: ', message)
    print('----------------NONLOCAL------------------')
    print('global message: ', message)
    enclosing_nonlocal()
    print('global message: ', message)
    print('----------------GLOBAL--------------------')
    print('global message: ', message)
    enclosing_global()
    print('global message: ', message)
    print('------------------------------------')

"""
Output:

------------------------------------
global message:  global
enclosing message:  enclosing
enclosing message:  enclosing
global message:  global
----------------NONLOCAL------------------
global message:  global
enclosing message:  enclosing
enclosing message:  local
global message:  global
----------------GLOBAL--------------------
global message:  global
enclosing message:  enclosing
enclosing message:  enclosing
global message:  local
------------------------------------

"""

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