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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 _requirement_filter_by_marker(req):
 # type: (pkg_resources.Requirement) -> bool """Check if the requirement is satisfied by the marker. This function checks for a given Requirement whether its environment marker is satisfied on the current platform. Currently only the python version and system platform are checked. """

    if hasattr(req, 'marker') and req.marker:
        marker_env = {
            'python_version': '.'.join(map(str, sys.version_info[:2])),
            'sys_platform': sys.platform
        }
        if not req.marker.evaluate(environment=marker_env):
            return False
    return True