Do not assign a lambda expression, use a def (E731)
Lambdas should not be assigned to a variable. Instead, they should be defined as functions.
The primary reason for this is debugging. Lambdas show as <lambda>
in tracebacks, where functions will display the function’s name.
Anti-pattern
root = lambda folder_name: os.path.join(BASE_DIR, folder_name)
Best practice
def root(folder_name):
return os.path.join(BASE_DIR, folder_name)