python: Use trailing commas consistently.

Automatically generated by the following script, based on the output
of lint with flake8-comma:

import re
import sys

last_filename = None
last_row = None
lines = []

for msg in sys.stdin:
    m = re.match(
        r"\x1b\[35mflake8    \|\x1b\[0m \x1b\[1;31m(.+):(\d+):(\d+): (\w+)", msg
    )
    if m:
        filename, row_str, col_str, err = m.groups()
        row, col = int(row_str), int(col_str)

        if filename == last_filename:
            assert last_row != row
        else:
            if last_filename is not None:
                with open(last_filename, "w") as f:
                    f.writelines(lines)

            with open(filename) as f:
                lines = f.readlines()
            last_filename = filename
        last_row = row

        line = lines[row - 1]
        if err in ["C812", "C815"]:
            lines[row - 1] = line[: col - 1] + "," + line[col - 1 :]
        elif err in ["C819"]:
            assert line[col - 2] == ","
            lines[row - 1] = line[: col - 2] + line[col - 1 :].lstrip(" ")

if last_filename is not None:
    with open(last_filename, "w") as f:
        f.writelines(lines)

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

zerver/lib/zcommand.py

@@ -11,7 +11,7 @@ def process_zcommands(content: str, user_profile: UserProfile) -> Dict[str, Any]
         msg = 'Changed to {command} mode! To revert ' \
             '{command} mode, type `/{switch_command}`.'.format(
                 command=command,
-                switch_command=switch_command
+                switch_command=switch_command,
             )
         do_set_user_display_setting(user_profile=user_profile,
                                     setting_name=setting,