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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_agent_requirement_line(check, version):
 """ Compose a text line to be used in a requirements.txt file to install a check pinned to a specific version. """

    package_name = get_package_name(check)

    # no manifest
    if check in ('datadog_checks_base', 'datadog_checks_downloader'):
        return '{}=={}'.format(package_name, version)

    m = load_manifest(check)
    platforms = sorted(m.get('supported_os', []))

    # all platforms
    if platforms == ALL_PLATFORMS:
        return '{}=={}'.format(package_name, version)
    # one specific platform
    elif len(platforms) == 1:
        return "{}=={}; sys_platform == '{}'".format(package_name, version, PLATFORMS_TO_PY.get(platforms[0]))
    elif platforms:
        if 'windows' not in platforms:
            return "{}=={}; sys_platform != 'win32'".format(package_name, version)
        elif 'mac_os' not in platforms:
            return "{}=={}; sys_platform != 'darwin'".format(package_name, version)
        elif 'linux' not in platforms:
            return "{}=={}; sys_platform != 'linux2'".format(package_name, version)

    raise ManifestError("Can't parse the `supported_os` list for the check {}: {}".format(check, platforms))