Import statement inside class/function definition - is it a good idea?

I created a module named util that provides classes and functions I often use in Python. Some of them need imported features. What are the pros and the cons of importing needed things inside class/function definition? Is it better than import at the beginning of a module file? Is it a good idea?

It's the most common style to put every import at the top of the file. PEP 8 recommends it, which is a good reason to do it to start with. But that's not a whim, it has advantages (although not critical enough to make everything else a crime). It allows finding all imports at a glance, as opposed to looking through the whole file. It also ensures everything is imported before any other code (which may depend on some imports) is executed. NameErrors are usually easy to resolve, but they can be annoying.

There's no (significant) namespace pollution to be avoided by keeping the module in a smaller scope, since all you add is the actual module (no, import * doesn't count and probably shouldn't be used anyway). Inside functions, you'd import again on every call (not really harmful since everything is imported once, but uncalled for).

PEP8, the Python style guide, states that:

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

Of course this is no hard and fast rule, and imports can go anywhere you want them to. But putting them at the top is the best way to go about it. You can of course import within functions or a class.

But note you cannot do this:

def foo():
    from os import *

Because:

SyntaxWarning: import * only allowed at module level