Accept plural fields (user_ids, channels, types) as Lists (#274)

* Updated docs to add rate limiting references
* Convert plural field values to strings if needed
* Added test for converting plural fields to CSV

Author: Roach

slackclient/slackrequest.py

@@ -76,6 +76,13 @@ def do(self, token, request="?", post_data=None, domain="slack.com", timeout=Non
         # Only do this for requests that are UPLOADING files; downloading files
         # use the 'file' argument to point to a File ID.
         post_data = post_data or {}
+
+        # Check for plural fields and convert them to comma-separated strings if needed
+        for field in {'channels', 'users', 'types'} & set(post_data.keys()):
+            if isinstance(post_data[field], list):
+                post_data[field] = ",".join(post_data[field])
+
+        # Move singular file objects into `files`
         upload_requests = ['files.upload']
 
         files = None

tests/test_slackrequest.py

@@ -42,6 +42,18 @@ def test_auth_header(mocker):
     assert "Bearer xoxb-123" in kwargs['headers']['Authorization']
 
 
+def test_plural_field(mocker):
+    requests = mocker.patch('slackclient.slackrequest.requests')
+    request = SlackRequest()
+
+    request.do('xoxb-123','conversations.open', {'users': ['U123', 'U234', 'U345']})
+    args, kwargs = requests.post.call_args
+
+    assert requests.post.call_count == 1
+    assert 'https://slack.com/api/conversations.open' == args[0]
+    assert kwargs['data'] == '{"users": "U123,U234,U345"}'
+
+
 def test_post_file(mocker):
     requests = mocker.patch('slackclient.slackrequest.requests')
     request = SlackRequest()