Scope of imported modules/functions in Python

Question

I'm new here and am not 100% sure how to ask this question so I'll just dive right in. Should I be using import statements at the beginning of every function I write that import all of the various modules/functions I need for that function's scope? i.e.

def func1()
    import os.path
    print func(2)
    do something with os.path

def func2()
    import os.path
    do something with os.path

Will this increase memory overheads, or other overheads, or is the import statement just mapping a local name to an already loaded object? Is there are better way to do this? (Links to tutorials etc. most welcome. I've been looking for a while but can't find a good answer to this.)

@S. Lott. The topvoted answer to that question is technically wrong. I added a new on to it. The problem is that the timing technique used is very flawed and doesn't account for the difference in cost between accessing a local and accessing a global. — aaronasterling
– aaronasterling, Commented Jan 25, 2011 at 4:41

miku · Accepted Answer · 2014-02-04 12:41:43Z

10

Usually all imports are placed at the beginning of the file. Importing a module in a function body will import a module in that scope only:

def f():
    import sys
    print 'f', sys.version_info

def g():
    print 'g', sys.version_info

if __name__ == '__main__':
    f() # will work
    g() # won't work, since sys hasn't been imported into this modules namespace

edited Feb 4, 2014 at 12:41

answered Jan 25, 2011 at 3:42

miku

189k47 gold badges314 silver badges317 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

variable Over a year ago

I mean, is sys.modules per thread or per process or per computer?

Ignacio Vazquez-Abrams · Accepted Answer · 2011-01-25 03:36:00Z

8

The module will only be processed the first time it is imported; subsequent imports will only copy a reference to the local scope. It is however best style to import at the top of a module when possible; see PEP 8 for details.

answered Jan 25, 2011 at 3:36

Ignacio Vazquez-Abrams

804k160 gold badges1.4k silver badges1.4k bronze badges

1 Comment

mlissner Over a year ago

@GlenS: Learn PEP8. The sooner you do, the sooner your code will look right to other Python coders.

Collectives™ on Stack Overflow

Scope of imported modules/functions in Python

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related