The already-given answer works, but is unnecessarily clunky. An easier method:
import sys, os, importlib
sys.path.append(os.path.dirname(filename))
mname = os.path.splitext(os.path.basename(filename))[0]
imported = importlib.import_module(mname)
sys.path.pop()
imported is the imported module; you can use it as normal, through imported.method(arg). The final line isn't strictly necessary, but it's cleaner not to leave unnecessary entries in sys.path (particularly if you're going to run the code multiple times). This works in 3.4, and doesn't use anything marked as deprecated.