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up vote 3 down vote favorite

I have this code:

    lengths = []
    lengths.append(len(self.download_links))
    lengths.append(len(self.case_names))
    lengths.append(len(self.case_dates))
    lengths.append(len(self.docket_numbers))
    lengths.append(len(self.neutral_citations))
    lengths.append(len(self.precedential_statuses))

Unfortunately, any of those object properties can be None, so I need to check each with either an if not None block or a try/except block. Checking each individually will blow up the size and conciseness of the code.

I assume there must be a better way for this kind of pattern, right?

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2 Answers 2

up vote 5 down vote accepted

Firstly, consider whether these shouldn't be None, but instead should be empty lists. Most of the time None is better replaced by something else like an empty list.

If that's not an option, you can use a list:

for item in [self.download_links, self.case_name...]:
    if item is not None:
         length.append( len(item) )

or a function

def add_length(obj):
   if obj is not None:
            lengths.append(len(obj))

add_length(self.download_links)
add_length(self.case_name)
...
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I think None is better semantically in this case than [], but this will do it, and makes sense, thanks. –  mlissner Feb 24 '12 at 19:50
    
@mlissner: If something could be None or a list I'd say it's a bad design choice. –  Rik Poggi Mar 5 '12 at 12:31
up vote 0 down vote

Why not just try some list comprehensions:

chunks = [self.download_links, self.case_name...]
lengths = [len(i) for i in chunks if i is not None]
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