Is it pythonic to import inside functions?

python conventions
codeape picture codeape · Jun 21, 2009 · Viewed 50.8k times · Source

PEP 8 says:

  • Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants.

On occation, I violate PEP 8. Some times I import stuff inside functions. As a general rule, I do this if there is an import that is only used within a single function.

Any opinions?

EDIT (the reason I feel importing in functions can be a good idea):

Main reason: It can make the code clearer.

  • When looking at the code of a function I might ask myself: "What is function/class xxx?" (xxx being used inside the function). If I have all my imports at the top of the module, I have to go look there to determine what xxx is. This is more of an issue when using from m import xxx. Seeing m.xxx in the function probably tells me more. Depending on what m is: Is it a well-known top-level module/package (import m)? Or is it a sub-module/package (from a.b.c import m)?
  • In some cases having that extra information ("What is xxx?") close to where xxx is used can make the function easier to understand.

Answer

Peter Ericson picture Peter Ericson · Jun 22, 2009

In the long run I think you'll appreciate having most of your imports at the top of the file, that way you can tell at a glance how complicated your module is by what it needs to import.

If I'm adding new code to an existing file I'll usually do the import where it's needed and then if the code stays I'll make things more permanent by moving the import line to the top of the file.

One other point, I prefer to get an ImportError exception before any code is run -- as a sanity check, so that's another reason to import at the top.

I use pyChecker to check for unused modules.

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