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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(package_str, classname):
    '''Retrieve from the internal cache a class instance. All arguments are case-insensitive''' 
    if (package_str in _dynamo_cache) and (classname in _dynamo_cache[package_str]):
        return _dynamo_cache[package_str][classname]
    return None