typo in "action" creates hard to diagnose error message

The following contains a typo 

import argparse 
parser = argparse.ArgumentParser(prog="abc") 
parser.add_argument("--version", action="store-true") 
args = parser.parse_args() 

See it? I did "store-true" instead of "store_true". When I run the 
code I get 

Traceback (most recent call last): 
  File "problem.py", line 6, in <module> 
    parser.add_argument("--version", action="store-true") 
  File "/Users/dalke/tmp/argparse.py", line 1264, in add_argument 
    action = action_class(**kwargs) 
TypeError: 'str' object is not callable 

I spent some time trying to figure out what I did wrong, before 
spotting the "-" instead of the "_" in my code. 

Reading the documentation and the code, it appears the goal is to use 
strings for most of the cases but also allow argparse users to 
"specify an arbitrary action by passing an object that implements the 
Action API". 

However, strings are not and cannot implement the Action API. Passing 
in an unrecognized string will always be an error, and likely be a 
typo like mine. 

Could you check for the case of passing in an unsupported string and 
raise an exception with a more useful error message?

Original issue reported on code.google.com by andrewda...@gmail.com on 18 Oct 2009 at 8:02

zenlotus / argparse

typo in "action" creates hard to diagnose error message #39