IndentedBlock causes parse actions of its first element to be called twice

[Honza0297]

Sorry for opening another issue in a short time, but:

When the first element of IndentedBlock has a parse action (entry1 and its e1_action in the example), it is performed twice:

def e1_action(x):
    print("entry1")
entry1 = Keyword("entry1").set_parse_action(e1_action)

def e2_action(x):
    print("entry2")
entry2 = Keyword("entry2").set_parse_action(e2_action)

entries = IndentedBlock(entry1 | entry2, recursive=True, grouped=True)
header = Keyword("header") + Word(alphanums + "_") + entries


s = """
header foo
    entry1
    entry2"""
header.parse_string(s)

Expected result:

entry1
entry2

Actual result:

entry1
entry1
entry2

I tried to dig into it and found out that it is caused by this line: self.expr.try_parse(instring, anchor_loc, do_actions=doActions), specifically by do_actions=doActions.
I hotfixed it locally to do_actions=False (I would expect not to perform parse action when I am only trying to parse the block and will parse it again) and now, the output is as expected (by me :)) .
Is it truly a bug or (rather strange) feature?

Thanks for your answer in advance!

[ptmcg]

You can also prevent double evaluation of the parse action by enabling packrat parsing.

ParserElement.enable_packrat()

This will cache the result of the try_parse lookahead, so that when it succeeds, the actual parse doesn't repeat the parsing and parse action, but just retuns the value from the packrat cache.