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pythonpython-3.xpep8

How to pass a constant variable to a function

which one is a better design in the following scenario and why?

A:

stop_words = ['com1', 'com2'] 
    
def clean_text(text_tokens, stop_words):
    return [token for token in text_tokens if token not in stop_words]

clean_text(['hello', 'world', 'com1', 'com2'], stop_words)

B:

def clean_text(text_tokens):
    stop_words = ['com1', 'com2']
    return [token for token in text_tokens if token not in stop_words]

clean_text(['hello', 'world', 'com1', 'com2'])

C:

STOP_WORDS = ['com1', 'com2'] 
    
def clean_text(text_tokens):
    return [token for token in text_tokens if token not in STOP_WORDS]

clean_text(['hello', 'world', 'com1', 'com2'])

Added C version based on @MisterMiyagi answer.

Note1: In this context, stop_words is fixed and does not change.

Note2: stop_words can be a small or a very large list.

Solution

  • Middle ground: use a default value for the argument.

    def clean_text(text_tokens, stop_words={'com1', 'com2'}):
    return [token for token in text_tokens if token not in stop_words]

clean_text(['hello', 'world', 'com1', 'com2'])

    Now the constant {'com1', 'com2'} is only created once (when the function is defined); it doesn't pollute the global scope; and if you end up wanting to, you can optionally pass different stop_words when you call clean_text.