inside of myfile.py insert an __import__
module = __import__(sys.argv[1].replace('.py', ''))
will import the first command line argument as module which you can then use as any other module that was imported. The return value from __import__ is a module.
Really in python, import mod is just a shorthand for mod = __import__('mod'), and you are allowed to call the __import__ function if you do so choose.
An example:
>>> module = __import__("math") #same as "import math as module"
>>> module.sqrt(16)
4.0
If you wish to pollute your global namespace with the contents of the command line argument, you can read about how to do a from * import here:
How does one do the equivalent of "import * from module" with Python's __import__ function?