Python: Global Variable Access

Current post is on how to access the global variables in Python 3.2. 

Global variables can be easily accessed by using the keyword global.

According to Python 3.2 documentation:

The global statement is a declaration which holds for the entire current code block. It means that the listed identifiers are to be interpreted as globals. It would be impossible to assign to a global variable without global, although free variables may refer to globals without being declared global.

Names listed in a global statement must not be used in the same code block textually preceding that global statement.

Names listed in a global statement must not be defined as formal parameters or in a for loop control target, class definition, function definition, or import statement.

Example 1: Change the global variable

globalVariable = False

def ChangeGlobalFunction():
      """Function that changes global variable"""
      global  globalVariable  #Global statement
      globalVariable = True

def PrintGlobalFunction():
      """Function that prints global variable"""
      print(globalVariable)

PrintGlobalFunction()
ChangeGlobalFunction()
PrintGlobalFunction()

Output:

False
True

Python: Check for file existence

Current post is on how to check whether file exists on system running Python 3.2.

First import the 'os.path' module.  os.path module implements some useful functions on pathname.

import os.path

Add the following line to check file.
  
os.path.exists(filename)

It returns True if filename exists else returns False


To make sure it is file and it exists, one can use:

os.path.isfile(filename)

It returns True only if the type is of file and it exists else returns False

Example 1: File Check using 'exists' function

      if os.path.exists("HelloWorld.py"):
           print("Hello World")
      else:
           print("No World !!!")

Example 2: File Check using 'isfile' function

      if os.path.isfile("HelloWorld.py"):
           print("Hello World")
      else:
           print("No World !!!")