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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_function(fn_name):
 """Retrieve the function defined by the function_name. Arguments: fn_name: specification of the type module:function_name. """

    module_name, callable_name = fn_name.split(':')
    current = globals()
    if not callable_name:
        callable_name = module_name
    else:
        import importlib
        try:
            module = importlib.import_module(module_name)
        except ImportError:
            log.error("failed to import %s", module_name)
            raise
        current = module
    for level in callable_name.split('.'):
        current = getattr(current, level)
    code = current.__code__
    if code.co_argcount != 2:
        raise ValueError('function should take 2 arguments: lines, file_name')
    return current