Understanding Python’s “global name is not defined” Error

If you have been working with Python for a while, you might have come across the error message “global name is not defined”. This error typically occurs when you try to access a variable or function that has not been defined or is not in scope. In this article, we will explore the reasons behind this error and discuss how to resolve it.

What does “global name is not defined” mean?

When you see the error message “global name is not defined”, it means that Python cannot find a variable or function with the specified name in the current scope. This can happen for several reasons, including:

1. The variable or function has not been defined at all.
2. The variable or function is defined in a different scope and is not accessible in the current scope.
3. There is a typo or misspelling in the variable or function name.

Let’s take a closer look at each of these scenarios and see how we can resolve them.

Scenario 1: Variable or function not defined

The most common reason for the “global name is not defined” error is that the variable or function you are trying to access has not been defined at all. This can happen if you forget to define the variable or function before using it.

For example, consider the following code snippet:

def calculate_area(length, width):
    return length * width

print(calculate_area(5, 10))
print(calculate_perimeter(5, 10))

In this code, we define a function calculate_area that calculates the area of a rectangle. We then try to call this function and print the result. However, we also try to call a function calculate_perimeter that has not been defined. This will result in the “global name ‘calculate_perimeter’ is not defined” error.

To fix this error, you need to make sure that all variables and functions are defined before using them. In this case, you can either define the calculate_perimeter function or remove the line that tries to call it.

Scenario 2: Variable or function in a different scope

Another reason for the “global name is not defined” error is that the variable or function you are trying to access is defined in a different scope and is not accessible in the current scope.

In Python, variables and functions have different scopes, such as global scope, local scope, and function scope. If you try to access a variable or function that is defined in a different scope, Python will raise the “global name is not defined” error.

Consider the following code snippet:

def calculate_area(length, width):
    result = length * width
    return result

print(calculate_area(5, 10))
print(result)

In this code, we define a function calculate_area that calculates the area of a rectangle and stores the result in a variable result. We then try to print the value of result outside the function. However, since result is defined in the local scope of the function, it is not accessible outside the function. This will result in the “global name ‘result’ is not defined” error.

To fix this error, you need to make sure that you are accessing variables and functions in the correct scope. In this case, you can either move the print(result) statement inside the calculate_area function or return the value of result from the function and assign it to a variable in the global scope.

Scenario 3: Typo or misspelling

Sometimes, the “global name is not defined” error can occur due to a simple typo or misspelling in the variable or function name. Python is case-sensitive, so even a small difference in capitalization can result in this error.

Consider the following code snippet:

def calculate_area(length, width):
    return length * width

print(calculate_area(5, 10))
print(calculate_Area(5, 10))

In this code, we define a function calculate_area that calculates the area of a rectangle. However, when we try to call the function with a capitalized A in calculate_Area, Python will raise the “global name ‘calculate_Area’ is not defined” error.

To fix this error, you need to make sure that you are using the correct spelling and capitalization when accessing variables and functions. In this case, you can simply change calculate_Area to calculate_area to match the function name.

To resolve this error, you need to ensure that all variables and functions are defined before using them, access variables and functions in the correct scope, and use the correct spelling and capitalization. By understanding the reasons behind this error and following these guidelines, you can avoid and fix the “global name is not defined” error in your Python code.