human
Complete the below
@directive('versions')
def version(ver, checksum=None, **kwargs):

    ''''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.'
    '''
 ... Can you provide a the Python program you requested?
assistant
#Here is the Python program you requested.
    def _execute(pkg):
        if checksum:
            kwargs['md5'] = checksum
        pkg.versions[Version(ver)] = kwargs
    return _execute