Improve argument handling in powerline script

Modules can now be any string, and an informative error message will be
written to sys.stdout if the module doesn't exist. The
`last_pipe_status` argument will also automatically be split into
a list.

powerline/segments/shell.py

@@ -7,10 +7,9 @@ def last_status(segment_info):
 
 
 def last_pipe_status(segment_info):
-	pipe_status = [int(status) for status in segment_info.last_pipe_status.split()]
-	if any(pipe_status):
+	if any(segment_info.last_pipe_status):
 		return [{"contents": str(status), "highlight_group": "exit_fail" if status else "exit_success"}
-			for status in pipe_status]
+			for status in segment_info.last_pipe_status]
 	else:
 		return None
 last_pipe_status.requires_powerline_segment_info = True

scripts/powerline

@@ -14,10 +14,10 @@ except ImportError:
 parser = argparse.ArgumentParser(description=__doc__)
 parser.add_argument('ext', nargs=1)
 parser.add_argument('side', nargs='?', choices=('left', 'right'))
-parser.add_argument('-r', '--renderer_module', choices=('shell', 'zsh_prompt', 'tmux'))
+parser.add_argument('-r', '--renderer_module', metavar='MODULE', type=str)
 parser.add_argument('-w', '--width', type=int)
-parser.add_argument('--last_exit_code', type=int, metavar='INT')
-parser.add_argument('--last_pipe_status', metavar='LIST')
+parser.add_argument('--last_exit_code', metavar='INT', type=int)
+parser.add_argument('--last_pipe_status', metavar='LIST', default='', type=lambda s: [int(status) for status in s.split()])
 
 if __name__ == '__main__':
 	args = parser.parse_args()