Four Tricks for Comprehensions in Python

jieforest

and use it like that:

1. >>> first_chars = list(word[0] for word in text.split() if stopif(word == "and"))
   
2. >>> first_chars
   
3. ['I', 'c', 't', 't', 'd', 'b', 'W', 'b']
   

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Both version are a bit lacking in elegance and may be surprising to an unsuspecting reader, but I personally find the if <expr> else stop() intuitive enough to actually use.

Just for completeness: You might use itertools.takewhile() to achieve the same effect.

1. >>> first_chars = [word[0] for word in itertools.takewhile(lambda word: word != "and", text.split())]
   
2. >>> first_chars
   
3. ['I', 'c', 't', 't', 'd', 'b', 'W', 'b']
   

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jieforest

It's up to you to decide what you find more readable. When in doubt, always chose the explicit loop.

Wrapping Up

Comprehensions and Generator Expressions are fun little constructs. Though (intentionally) limited in its expressiveness, they support and complement the functional features of the language and the standard library.

I have not given up hope that one day we will get proper “breaking” syntax (any attempts so far have been shot down at the python-ideas mailing list), but even as limited as they are – {list,set,dict} comprehensions and generator expressions are among my favorite syntactical features in Python.

Thanks for reading this article. Happy Coding!

jieforest

over.