human
Solve the following python programming problem given the following code:
@directive('versions')
def version(ver, checksum=None, **kwargs):
assistant
#Here is the Python program you requested.

    """Adds a version and metadata describing how to fetch it.
    Metadata is just stored as a dict in the package\s versions
    dictionary.  Package must turn it into a valid fetch strategy
    later.
    """
    def _execute(pkg):
        if checksum:
            kwargs['md5'] = checksum
        pkg.versions[Version(ver)] = kwargs
    return _execute