Python - recursive function returns None

Question

I'm trying to sanitise the URL, and extract only Id's from it (by skipping the URL part). By doing some debugging, I can see the value im looking for is printing, however, not returning (or returns None)

This is the code:

def _sanitize_urls(urls=None):
    redact_list = [
        ("abcd.google.com", 3),
        ("xyz.yahoo.com", 4),
    ]
    urls_sanitized = []
    redact_found = [redact for redact in redact_list if redact[0] in urls]
    if redact_found:
        urls = urls.split(" ")
        print(urls)
        urls_sanitized = [
            words.split("/")[redact_found[0][1]] if redact_found[0][0] in words else words for words in urls
        ]
        print(urls_sanitized)
        urls_sanitized = " ".join(urls_sanitized)
        print(urls_sanitized)
        redact_found = [redact for redact in redact_list if redact[0] in urls_sanitized]
        print(redact_found)
        if not redact_found:
            print(urls_sanitized)
            return urls_sanitized
        else:
            _sanitize_urls(urls_sanitized)


def main():
    urls = "https://abcd.google.com/ID-XXXX and https://xyz.yahoo.com/Id/ID-XXXX"
    redact_exists = _sanitize_urls(urls)
    print(redact_exists)


if __name__ == "__main__":
    main()

Output Im expecting is => "ID-XXXX and ID-XXXX". Output I'm getting right now is None.

With some debugging on my side =>

['https://abcd.google.com/ID-XXXX', 'and', 'https://xyz.yahoo.com/Id/ID-XXXX']
['ID-XXXX', 'and', 'https://xyz.yahoo.com/Id/ID-XXXX']
ID-XXXX and https://xyz.yahoo.com/Id/ID-XXXX
[('xyz.yahoo.com', 4)]
['ID-XXXX', 'and', 'https://xyz.yahoo.com/Id/ID-XXXX']
['ID-XXXX', 'and', 'ID-XXXX']
ID-XXXX and ID-XXXX
[]
ID-XXXX and ID-XXXX
None

As you can see, print, prints the correct value, till the last moment, however its not returning to main function, rather returning None. Any ideas?

you have to return the output of the recursive call: `return _sanitize_urls(urls_sanitized)` — Nick, May 09 '20 at 04:21

score 1 · Accepted Answer · answered May 09 '20 at 04:16

1

In the last line of your _sanitize_urls function, you have

 _sanitize_urls(urls_sanitized)

There's no more code to your function after this. In Python, if a function runs out of code without an explicit return statement, None will be returned automatically.

answered May 09 '20 at 04:16

Daniel Walker

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Thanks Daniel. That fixed it. And good to know why its happening. – Danny May 09 '20 at 04:39

Python - recursive function returns None

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