How is calling module and function by string handled in python?

Question

Calling a function of a module from a string with the function's name in Python shows us how to call a function by using getattr("bar")(), but this assumes that we have the module foo imported already.

How would would we then go about calling for the execution of "foo.bar" assuming that we probably also have to perform the import of foo (or from bar import foo)?

Answer 1

Use the __import__(....) function:

http://docs.python.org/library/functions.html#import

(David almost had it, but I think his example is more appropriate for what to do if you want to redefine the normal import process - to e.g. load from a zip file)

Answer 2

You can use find_module and load_module from the imp module to load a module whose name and/or location is determined at execution time.

The example at the end of the documentation topic explains how:

import imp
import sys

def __import__(name, globals=None, locals=None, fromlist=None):
    # Fast path: see if the module has already been imported.
    try:
        return sys.modules[name]
    except KeyError:
        pass

    # If any of the following calls raises an exception,
    # there's a problem we can't handle -- let the caller handle it.

    fp, pathname, description = imp.find_module(name)

    try:
        return imp.load_module(name, fp, pathname, description)
    finally:
        # Since we may exit via an exception, close fp explicitly.
        if fp:
            fp.close()