import requests

apiurl = "http://en.wikipedia.org/w/api.php"

params = {'action': 'query',
          'format': 'json',
          'list': 'categorymembers',
          'cmtitle': 'Category:Gastropods_described_in_1999',
          'cmtype': 'page',
          'cmlimit': 300,
          'cmsort': 'sortkey',
          'cmstartsortkeyprefix': 'H',
          'cmendsortkeyprefix': 'I', }

# Request with cmlimit big enough to accomodate all expected results
rsponse = requests.get(url=apiurl, params=params)
print('###### Everything beginning with H in one gulp ######')
print(rsponse.json())

# reduce cmlimit and iterate with continue parameters
print('###### Using cmlimit=20 ######')

params['cmlimit'] = 20
complete = ''
iteration = 1

while complete == '':
   rsponse = requests.get(url=apiurl, params=params)
   json = rsponse.json()
   print('>>>> iteration=' + str(iteration) + ' <<<<')
   print(json)
   if (json.get('continue')):
      for contkey, value in json['continue'].items():
            params[contkey] = value
   else:
      complete = 'complete'
   iteration = iteration + 1