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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 requirements(requirements_file):
 """Return packages mentioned in the given file. Args: requirements_file (str):
 path to the requirements file to be parsed. Returns: (list):
 3rd-party package dependencies contained in the file. """

    return [
        str(pkg.req) for pkg in parse_requirements(
            requirements_file, session=pip_download.PipSession()) if pkg.req is not None]