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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 check_requirements_file(req_file, skip_packages):
 """Return list of outdated requirements. Args: req_file (str):
 Filename of requirements file skip_packages (list):
 List of package names to ignore. """

    reqs = read_requirements(req_file)
    if skip_packages is not None:
        reqs = [req for req in reqs if req.name not in skip_packages]
    outdated_reqs = filter(None, [check_req(req) for req in reqs])
    return outdated_reqs