Monday, March 31, 2014

execfile and imported modules

I was given to believe that Python's execfile statement simply executed all the commands in a file and continued on its way. This is not entirely true, at least in Python 2.7: imported modules seem not to be handled by the execfile statement, which seems to be rather odd to me.

import numpy


def gen(n=100):
  return numpy.arange(n)

This code does what you expect when you import it as a module:

In [1]: import test

In [2]: test.gen(10)
Out[2]: array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

And when you run it as a script to incorporate it into your workspace:

In [3]: run test

In [4]: gen(10)
Out[4]: array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

However, when you use execfile to run the script you run into a snag:


In [5]: pars = {}; execfile('test.py', {}, pars); pars['gen'](10)
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-5-b06061c74d2b> in <module>()
----> 1 pars = {}; execfile('test.py', {}, pars); pars['gen'](10)
/Users/kghose/Code/Mitty/Test/test.py in gen(n)
      3 
      4 def gen(n=100):
----> 5   return numpy.arange(n)
NameError: global name 'numpy' is not defined

Whaaaaa?

If, instead, you use the fascinating standard Python imp module, you get:


In [7]: import imp; mod = imp.load_source('test','./test.py', open('test.py','r'))
In [8]: mod
Out[8]: <module 'test' from './test.pyc'>
In [9]: mod.gen(10)
Out[9]: array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

Things run as they should.

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