Python statements can access variables in both the local namespace and in the global namespace. When a local and a global variable have the same name, the local variable "shadows" or "hides" the global variable. When the variable is referenced, the variable with local scope is used unless you explicitly use the global statement to reference the global variable. This can lead to confusion as a reader of the code may expect the variable to refer to a global.

Avoid using the same name for variables in local and global namespaces.

The following simple example shows how a local variable can "shadow" a global variable. The local variable should be renamed to make the code easier to interpret.

J. Lusth, The Art and Craft of Programming - Python Edition, Section: Scope. University of Alabama, 2012. (Published online).

Python Language Reference: The global statement.