TRIVIA: Windows 8

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.

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 !!!")

Python: Message Box in Windows

Current post is on how to show message box in Python 3.2 running on Microsoft Windows OS.

First import the 'ctypes' module. ctypes module provides C compatible data types and allows calling functions in DLLs or shared libraries.

import ctypes

Next we need is the messagebox function pointer

messageBox = ctypes.windll.user32.MessageBoxW *

After having the function pointer, we just need to call the function with required arguments.

returnValue = messageBox(ParentHandle,Error Text,Title Text,ButtonEnumValue)

where,
           ParentHandle = Handle to parent window
           Error Text = Text one wants to show to end user
           Title Text = Text that will appear on Title bar of message box
           ButtonEnumValue = Which button one needs to show

Detailed information can be found on Microsoft MessageBox Documentation

Based on return value, one can take the required action.

Example 1: Message Box with OK button.

import ctypes

messageBox = ctypes.windll.user32.MessageBoxW

returnValue = messageBox(None,"Message Box!!!","Hello",0x40 | 0x0)

Example 2: Message Box with OK-Cancel button & ReturnValue Check