paul j3 <ajipa...@gmail.com> added the comment:

This is a consequence of Python's own definition of append vs extend

In [730]: alist = []                                                            
                       
In [731]: alist.append('astring')                                               
                       
In [732]: alist                                                                 
                       
Out[732]: ['astring']
In [733]: alist.extend('astring')                                               
                       
In [734]: alist                                                                 
                       
Out[734]: ['astring', 'a', 's', 't', 'r', 'i', 'n', 'g']
In [735]: alist.extend(['astring'])                                             
                       
In [736]: alist                                                                 
                       
Out[736]: ['astring', 'a', 's', 't', 'r', 'i', 'n', 'g', 'astring']

Normally 'add_argument' doesn't check for valid parameters, but some Action 
subclasses do their own checking, 

'extend' inherits the nargs==0 test from 'append'. (extend just modifies the 
__call__, not the __init__ method.

But I wonder, was this situation discussed in the original bug/issue?

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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue40365>
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