Why is it Important to Use the Global Keyword to Modify Global Variables in Functions?

Understanding Global Variable Modification in Functions

In programming, global variables are shared among all functions within a program. Modifying a global variable inside a function should reflect its change throughout the program. However, certain circumstances can lead to unexpected behavior, as highlighted in the following scenario.

The Problem:

Given the code snippet below:

<code class="python">done = False

def function():
    for loop:
        code
        if not comply:
            done = True  #let's say that the code enters this if-statement

while done == False:
    function()</code>

The code seems to attempt to exit the while loop when the done variable is set to True within the function. However, the issue arises when the function() does not properly modify the global done variable, resulting in the while loop continuing indefinitely.

The Solution:

The problem lies in the function's scope. Functions create their own namespace, meaning the done variable within function() is created locally and not the same as the global done variable. To access and modify the global done variable, the global keyword must be used:

<code class="python">def function():
    global done
    for loop:
        code
        if not comply:
            done = True</code>

Using global done ensures that changes to the done variable made within function() affect the global variable, triggering the exit from the while loop when it is set to True.

Explanation:

The global keyword is used to declare and modify global variables from within a local scope, such as a function. It allows the function to work with the original variable instead of creating a new local copy. By using global done, the function can modify the global done variable, making its changes accessible outside the function.

The above is the detailed content of Why is it Important to Use the Global Keyword to Modify Global Variables in Functions?. For more information, please follow other related articles on the PHP Chinese website!