How Do I Use Global Variables Effectively Within and Across Python Functions?

Using Global Variables Within Functions

In Python, variables defined within a function are local to that function. However, sometimes it is necessary to access or modify a variable across multiple functions. This is where global variables come into play.

Creating and Declaring Global Variables

To create a global variable within a function, you must use the global keyword. This keyword must be used before assigning a value to the variable:

globvar = 0

def set_globvar_to_one():
    global globvar  # Declares globvar as a global variable
    globvar = 1

Important Note: The global keyword is only required when modifying the value of the global variable. It is not necessary when accessing its value.

Using Global Variables in Other Functions

Once a global variable is declared within one function, you can use it in other functions by simply referencing its name:

def print_globvar():
    print(globvar)  # No global declaration is required to read the variable

Example: Setting and Reading a Global Variable

Consider the following example:

globvar = 0

def set_globvar_to_one():
    global globvar
    globvar = 1

def print_globvar():
    print(globvar)

set_globvar_to_one()
print_globvar()  # Prints 1

In this example, globvar is set to 1 in the set_globvar_to_one function, and the value is then printed in the print_globvar function.

Cross-Module Sharing of Global Variables

It is important to note that global variables are only shared within the current module. If you want to share a global variable across multiple modules, you can use the __init__.py file in the parent directory to define the variable and import it into the desired modules.

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