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Date: Tue, 07 Feb 2012 21:05:15 -0500
From: Dave Angel <d@davea.name>
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To: Lei Cheng <pat.inside@gmail.com>
Subject: Re: when to use import statements in the header, when to use import statements in the blocks where they are used?
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On 02/07/2012 08:48 PM, Lei Cheng wrote:
> Hi all,
>
>     In a py file, when to use import statements in the header, when to use
> import statements in the blocks where they are used?
>     What are the best practices?
>     Thanks!
>
> Pat
>
Best practice is to put all the imports at the beginning of the module, 
so they are easy to spot.

If you put an import inside a function, it gets re-executed each time 
the function is called, which is a waste of time.  Not too much, since 
import first checks sys.modules to see if it's already loaded.

Also, avoid the     from xxx import *    form, as it pollutes the 
namespace.  And it makes it hard to figure out where a particular name 
is declared.

I believe these and other best practices can be found in pep8.

http://www.python.org/dev/peps/pep-0008/

-- 

DaveA