15.3 Importing a Dynamically Generated Module

Credit: Anders Hammarquist

15.3.1 Problem

You have code in either compiled or source form and need to wrap it in a module, possibly adding it to sys.modules as well.

15.3.2 Solution

We build a new module object, optionally add it to sys.modules, and populate it with an exec statement:

def importCode(code, name, add_to_sys_modules=0):
    """ code can be any object containing code -- string, file object, or
       compiled code object. Returns a new module object initialized
       by dynamically importing the given code and optionally adds it
       to sys.modules under the given name.
    """
    import imp
    module = imp.new_module(name)

    if add_to_sys_modules:
        import sys
        sys.modules[name] = module
    exec code in module._ _dict_ _

    return module

15.3.3 Discussion

This recipe lets you import a module from code that is dynamically generated or obtained. My original intent for it was to import a module stored in a database, but it will work for modules from any source. Thanks to the flexibility of the exec statement, the importCode function can accept code in many forms: a string of source (implicitly compiled), a file object (ditto), or a previously compiled code object, for example.

The addition of the newly generated module to sys.modules is optional. You shouldn't normally do this for such dynamically obtained code, but there are exceptions�for example, when import statements for the module's name are later executed, and it's important that they're retrieved from sys.modules. Note that if you want the sys.modules addition, it's best to perform it before the module's code body executes, just as normal import statements do, in case the code body relies on that normal behavior (which it normally doesn't, but it can't hurt to prepare for this).

Note that the normal Python statement:

import foo

is basically equivalent to:

if 'foo' in sys.modules:
    foo = sys.modules['foo']
else:
    foofile = open("/path/to/foo.py")
    foo = importCode(foofile, "foo", 1)

An example of using this recipe:

code = """
def testFunc(  ):
    print "spam!"

class testClass:
    def testMethod(self):
        print "eggs!"
"""

m = importCode(code,"test")
m.testFunc(  )
o = m.testClass(  )
o.testMethod(  )

15.3.4 See Also

Sections on the import and exec statements in the Language Reference; documentation on the modules attribute of the sys standard library module and the imp module in the Library Reference.