Is there a way to access parent modules in Python

12
votes

I need to know if there is a way to access parent modules from submodules. If I import submodule:

from subprocess import types

I have types - is there some Python magic to get access to subprocess module from types? Something similar to this for classes ().__class__.__bases__[0].__subclasses__().

4
pythonmoduleparent
Your example is weird -- types is actually the standard Python types module. Your import line will do the same as import types, and types will be exactly the same module object in both cases. – Sven Marnach
subprocess is not the "parent" of the types module in any sense that appears meaningful or useful to me. subprocess has evidently imported types, just like many other modules import types. What are you trying to do? What are you trying to do? – John Machin
I know that types is standard module, but I found it in subprocess modules when I search for all submodules. – jcubic
@John I try to block access to filesystem and the shell. – jcubic
@wizzwizz4 it was years ago that I learn this hard way, someone wipe out disk on my shared hosting. It was for my trypython.jcubic.pl I've needed to disable it but few years later I've found brython in js and now It use this library. – jcubic

4 Answers

7
votes

If you've accessed a module you can typically get to it from the sys.modules dictionary. Python doesn't keep "parent pointers" with names, particularly because the relationship is not one-to-one. For example, using your example:

>>> from subprocess import types
>>> types
<module 'types' from '/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/types.pyc'>
>>> import sys
>>> sys.modules['subprocess']
<module 'subprocess' from '/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.pyc'>

If you'll note the presence of types in the subprocess module is just an artifact of the import types statement in it. You just import types if you need that module.

In fact, a future version of subprocess may not import types any more, and your code will break. You should only import the names that appear in the __all__ list of a module; consider other names as implementation details.

So, for example:

>>> import subprocess
>>> dir(subprocess)
['CalledProcessError', 'MAXFD', 'PIPE', 'Popen', 'STDOUT', '_PIPE_BUF', '__all__', '__builtins__', '__doc__',
 '__file__', '__name__', '__package__', '_active', '_cleanup', '_demo_posix', '_demo_windows', '_eintr_retry_call',
 '_has_poll', 'call', 'check_call', 'check_output', 'errno', 'fcntl', 'gc', 'list2cmdline', 'mswindows', 'os',
 'pickle', 'select', 'signal', 'sys', 'traceback', 'types']
>>> subprocess.__all__
['Popen', 'PIPE', 'STDOUT', 'call', 'check_call', 'check_output', 'CalledProcessError']

You can see that most of the names visible in subprocess are just other top-level modules that it imports.

4
votes

For posterity, I ran into this also and came up with the one liner:

import sys
parent_module = sys.modules['.'.join(__name__.split('.')[:-1]) or '__main__']

The or '__main__' part is just in case you load the file directly it will return itself.

0
votes
full_module_name = module.__name__
parent, _, sub = full_module_name.rpartition('.')
if parent:
    parent = import(parent, fromlist='dummy')
-1
votes

I assume you are not inside the subprocess module already, you could do 

import somemodule
children = dir(somemodule)

Then you could inspect the children of subprocess with the inspect module: http://docs.python.org/library/inspect.html

Maybe the getmodule method would be useful for you? http://docs.python.org/library/inspect.html#inspect.getmodule

import inspect
parent_module = inspect.getmodule(somefunction)
children = dir(parent_module)
package = parent_module.__package__

On my machine __package__ returns empty for 'types', but can be more useful for my own modules as it does return the parent module as a string