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--help or  -h would do:

$ python pwb.py scripts/replicate_wiki.py -h
usage: replicate_wiki.py [-h] [-f FAMILY] [-r] [-o ORIGINAL_WIKI]
                         [-ns NAMESPACE] [-dns DEST_NAMESPACE]
                         destination [destination ...]

positional arguments:
  destination           destination wiki(s)

optional arguments:
  -h, --help            show this help message and exit
  -f FAMILY, --family FAMILY
                        wiki family
  -r, --replace         actually replace pages (without this option you will
                        only get an overview page)
  -o ORIGINAL_WIKI, --original ORIGINAL_WIKI
                        original wiki
  -ns NAMESPACE, --namespace NAMESPACE
                        specify namespace
  -dns DEST_NAMESPACE, --dest-namespace DEST_NAMESPACE
                        destination namespace (if different)