Force import from a function in another module

Question

Okay I'm trying to do something with python version 3.3.2 I'm trying to import module so I don't have to restart the shell. The following is just an example the final code will be able to change:

def importing():
    x = compile('import sys',"<string","exec")
    exec(x)
    return True

The problem with this is when I call on this using test.importing() it returns True but when i do sys it says:

 Traceback (most recent call last):
  File "<pyshell#74>", line 1, in <module>
    sys
NameError: name 'sys' is not defined

Whats confusing me is though it works perfectly fine in the shell, any ideas or advice would be very thankful to me.

user2234026: this is a very bad title! The point of the "python" tag is that you are having trouble with something in python! Your title should tell us the actual problem you are having! E.G., "Trouble with import in compile statement". — Andrew Jaffe, Jul 15 '13 at 06:49
Your problem seems almost identical to this one: http://stackoverflow.com/questions/951124/dynamic-loading-of-python-modules — mvherweg, Jul 15 '13 at 06:52

score 2 · Answer 1 · answered Jul 15 '13 at 06:48

2

if you just want to reload a module, you can do

from imp import reload
reload(sys)

answered Jul 15 '13 at 06:48

Fredrik Håård

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I wonder, though, why would you need to reload `sys`? It's not like you could change it, making a reload necessary... – Tim Pietzcker Jul 15 '13 at 06:49
Do we need to import reload? Isn't it a built in function? – Sudipta Jul 15 '13 at 07:02
1

In Python 2.x it's built in, but not in 3.x – Fredrik Håård Jul 15 '13 at 07:17
I assumed the sys-import was just a module guaranteed to be there, for testing purposes. – Fredrik Håård Jul 15 '13 at 13:09

score 2 · Answer 2 · answered Jul 15 '13 at 06:50

If you want to dynamically import modules you can use __import__.

Example Dive into Python:

>>> sys = __import__('sys')           
>>> os = __import__('os')
>>> re = __import__('re')
>>> unittest = __import__('unittest')
>>> sys                               
>>> <module 'sys' (built-in)>
>>> os
>>> <module 'os' from '/usr/local/lib/python2.2/os.pyc'>

score 1 · Answer 3 · answered Jul 15 '13 at 07:42

exec if no locals and globals passed, it executes in the current scope. So, your import sys import the sys module in the importing scope. See the code:

>>> def c():
...     exec('import sys')
...     print(locals())
...     print(globals())
... 
>>> c()
{'sys': <module 'sys' (built-in)>}
{'__builtins__': <module 'builtins'>, '__package__': None, '__name__': '__main__', '__loader__': <class '_frozen_importlib.BuiltinImporter'>, 'c': <function c at 0x7faa068e0320>, 'b': <function b at 0x7faa068e45f0>, 'a': <function a at 0x7faa066abe60>, 'd': <function d at 0x7faa068f6200>, 'inspect': <module 'inspect' from '/usr/lib64/python3.3/inspect.py'>, '__doc__': None}

See, the sys is in the local scope but not the global scope. But note, the import is excuted dynamically, even if it is in the local scope, you can not call the sys directly in the function. The call will end up with an error, can not find the sys in the global scope:

>>> def a():
...     exec('import sys')
...     if sys:
...             return True
...     else:   
...             return False
... 
>>> a()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in a
NameError: global name 'sys' is not defined

Instead, you should use locals():

>>> def b():
...     exec('import sys')
...     if locals()['sys']:
...             return True
...     else:
...             return False
... 
>>> b()
True

Last, I think using exec is not a good choice. Just like others have mentioned, using __importing__.

Force import from a function in another module

3 Answers3