Programatically importing a file and creating an instance of a class in Python

I have a (python) list of strings which refer to python source files and subsequently classes within those files which I want to import and then create an instance of the classes within the files (everything follows a strict naming convention, making this theoretically possible), in Ruby I would do something like:

require "lib/sources/#{source}.rb"
开发者_JAVA技巧s = source.constantize.new

How would I do something similar in Python?

Thanks, Ben

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Please see Dynamic Module Loading in Python:

If you have a need to import a module in python and, for whatever reason, you will not know the name of the module until run-time, python provides the built-in __import__ function.