title: Get custom fields for all users from Slack API
body: <p>This is my first python attempt and i'm trying to get a custom field for all Slack users. These fields are not available from the users.list feature so I need to run a users.profile.get for each ID in the users.list response and write the results to a file.</p>
  
  <p>I have managed to get this far but I need some hints/help to get further. How do i call users.profile.get for all IDs from users.list?</p>
  
  <pre><code>import os
  import io
  
  from slackclient import SlackClient
  
  slack_token = os.environ["SLACK_API_TOKEN"]
  sc = SlackClient(slack_token)
  
  if __name__ == '__main__':
      api_call = sc.api_call("users.list")
      if api_call.get('ok'):
          users = api_call.get('members')
          for user in users:
                  print(user['name'] + ' is : ' + user.get('id'))
  </code></pre>