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.
root = lambda folder_name: os.path.join(BASE_DIR, folder_name)
def root(folder_name): return os.path.join(BASE_DIR, folder_name)