A local name is redefining an argument, which might suggest a potential error. This is taken into account only for a handful of name binding operations, such as for iterations, with statements, and exception handler assignments.

Bad practice

def print_files(filename):
    with open(filename) as f:
        files = f.readlines()

    for filename in files:  # `filename` is already defined outside!
        print(filename)

Recommended

def print_files(filename):
    with open(filename) as f:
        files = f.readlines()

    for file in files:  # renamed it to `file` to avoid conflict
        print(file)