pyparsing delimitedList(..., combine=True) giving inconsistent result - pyparsing

Question

I'm using pyparsing==2.1.5 with Python 3.4, and I'm getting what seems to be an odd result:
word = Word(alphanums)
word_list_no_combine = delimitedList(word, combine=False)
word_list_combine = delimitedList(word, combine=True)
print(word_list_no_combine.parseString('one, two')) # ['one', 'two']
print(word_list_no_combine.parseString('one,two')) # ['one', 'two']
print(word_list_combine.parseString('one, two')) # ['one']: ODD ONE OUT
print(word_list_combine.parseString('one,two')) # ['one,two']
It's not obvious to me why the "combine" option causes one of the parts of the list to be swallowed when a space is present, but not when it's absent. Is this a pyparsing bug or am I missing something obvious?

Answer 1

Rather than modify pyparsing, I suggest you do this work using normal uncombined delimited list with a custom parse action:
word_list_combine_using_parse_action = word_list_no_combine.copy().setParseAction(','.join)
print(word_list_combine_using_parse_action.parseString('one, two'))
Will print one,two

Answer 2

Looks like it's due to the behaviour of Combine(), specifically its default "adjacent=True" option, which is then used by delimitedList():
class Combine(TokenConverter):
"""Converter to concatenate all matching tokens to a single string.
By default, the matching patterns must also be contiguous in the input string;
this can be disabled by specifying C{'adjacent=False'} in the constructor.
"""
def __init__( self, expr, joinString="", adjacent=True ):
# ...
def delimitedList( expr, delim=",", combine=False ):
# ...
dlName = _ustr(expr)+" ["+_ustr(delim)+" "+_ustr(expr)+"]..."
if combine:
return Combine( expr + ZeroOrMore( delim + expr ) ).setName(dlName)
else:
return ( expr + ZeroOrMore( Suppress( delim ) + expr ) ).setName(dlName)
So it can be solved with a replacement:
def delimitedListPlus(expr, delim=",", combine=False, combine_adjacent=False):
dlName = str(expr) + " [" + str(delim) + " " + str(expr) + "]..."
if combine:
return Combine(expr + ZeroOrMore(delim + expr),
adjacent=combine_adjacent).setName(dlName)
else:
return (expr + ZeroOrMore(Suppress(delim) + expr)).setName(dlName)