Omiting setResultsName in pyparsing expression

Question

Pyparsing documentation shows how to use setResultsName(...) method to set a resulting dictionary key. However, I saw a few times that this method is omitted and just (...) is used. What I mean is:

Instead of:

exp1 = pp.Word(pp.alphas).setResultsName('word1')
exp1.parseString( "Hello" ).asDict()

... one can do:

exp1 = pp.Word(pp.alphas)('word1')
exp1.parseString( "Hello" ).asDict()

... and the result is going to be exactly the same.

So 2 questions:

1. Where can I find the document confirming that omitting setResultsName can be done?

2. How does that work? Is pp.Word(pp.alphas), being a pyparsing object, a function? How is it implemented then?

Thanks

Answer 1

You can find the pyparsing documentation online.

The documentation for setResultsName says:

Define name for referencing matching tokens as a nested attribute of the returned parse results. NOTE: this returns a copy of the original ParserElement object; this is so that the client can define a basic element, such as an integer, and reference it in multiple places with different names.

You can also set results names using the abbreviated syntax, expr("name") in place of expr.setResultsName("name") - see __call__.

The information for __call__ confirms this behavior.

Since the ParserElement class implements __call__, that makes instances of that class callable, like a function. In this case, calling a ParserElement instance with a string argument is equivalent to calling setResultsName.