Ask YC: Best practice for Python module imports?

While technically Python doesn't import anything twice, it still takes nonzero time to check the module registry (a dictionary lookup). So if this happens every time your functions are called, it's unnecessary work, even if it's fast.

I personally tend to do all imports in one place, with the exception of test routines: I figure that a user of a module shouldn't really "depend" on modules that are only needed in test mode, so e.g. I would do a local "import" inside a _test() function.

Standard libraries I'm more likely to import globally, since I'm more likely to want to use them several times.

The most important thing is to figure out what works for you, and then be consistent about it.

I've learned a lot by looking at the source code for guido's rietveld: http://code.google.com/p/rietveld/source/browse/trunk/codere...

a, use your head, don't let convention override reason b, In general, keep module imports at the top of the file organized by type & package with the caveat that a large # of imports (say more than 10 or 20) may indicate the module is too ambitious and is a candidate for refactoring.

There's a section on imports.

from x import y

inside any function that needs y.

OTOH I think there are good reasons to go with the official Python recommendation, which another poster says states that all imports should be at the top on separate lines.