Re: [Pyparsing] Fwd: Returning an actual `list`

[<pt...@au...>]

I looked at this briefly last week, I thought I had a working example of this in the parsePythonValue.py example, but it seems to have the same problem.  

I thought I had worked out a working version at one time, using ungroup, but have not succeeded with that.

Here is an example of an expression and parse action that creates a list. Bear in mind that the return value from parseString is *always* a ParseResults, even if it is just `pp.pyparsing_common.integer.parseString("123")`.

Without the parse action, the parsed list is a ParseResults returned as the 0'th element of a ParseResults:

import pyparsing as pp

LBRACK, RBRACK = map(pp.Suppress, "[]")

item = pp.Word(pp.alphas)

list_expr = LBRACK + pp.delimitedList(item) + RBRACK

ret = pp.Group(list_expr).parseString("[a,b,c,d]")
print(ret)
print(type(ret))
print(ret[0])
print(type(ret[0]))

Gives:
[['a', 'b', 'c', 'd']]
<class 'pyparsing.ParseResults'>
['a', 'b', 'c', 'd']
<class 'pyparsing.ParseResults'>



Adding this parse action, we get a list returned as the 0'th element of a ParseResults. Note *no* Group around the list expression:

def make_list(tokens):
    contents = tokens.asList()
    tokens[:] = (contents,)

list_expr.addParseAction(make_list)
ret = list_expr.parseString("[a,b,c,d]")
print(ret)
print(type(ret))
print(ret[0])
print(type(ret[0]))

Gives:

[['a', 'b', 'c', 'd']]
<class 'pyparsing.ParseResults'>
['a', 'b', 'c', 'd']
<class 'list'>

Does that get you closer?

-- Paul

---- Athanasios Anastasiou <ath...@gm...> wrote: 
> Hello everyone
> 
> Any ideas on the attached?
> 
> All the best
> AA
> 
> 
> ---------- Forwarded message ----------
> From: Athanasios Anastasiou <ath...@gm...>
> Date: Wed, Oct 4, 2017 at 11:44 AM
> Subject: Returning an actual `list`
> To: pyp...@li...
> 
> 
> Hello
> 
> I have set up a very simple "primitive data type" parsing system to parse
> numbers, quoted strings, lists and dictionaries. The last two are following
> Python's convention.
> 
> While this is working, I am having trouble returning specific data types
> from the "action" of the LIST definition.
> 
> Here is a snippet:
> 
> LIST = pyparsing.Forward()
> DICT = pyparsing.Forward()
> 
> VALUE = (NUMBER|IDENTIFIER|DICT|pyparsing.Group(LIST))
> 
> KEY_VALUE_PAIR = pyparsing.Group(IDENTIFIER("key") +
> pyparsing.Suppress(":") + VALUE("value"))
> 
> LIST << pyparsing.Suppress("[") + pyparsing.delimitedList(VALUE) +
> pyparsing.Suppress("]")
> DICT << pyparsing.Suppress("{") + pyparsing.delimitedList(KEY_VALUE_PAIR) +
> pyparsing.Suppress("}")
> 
> So, when you are trying to parse something like: [1,2,3,4,[5,6]], this is
> returned as a pyparsing.ParseResults type of object, rather than a `list`.
> I have tried to set a simple parseAction with `lambda s,l,t: list(t)` or
> `lambda s,l,t:list(t[0])` but I am still getting back a ParseResults object.
> 
> Ideally, I would like the rule to return a list, just like the INT rule
> returns a proper Python integer.
> 
> Any ideas about what am I missing?
> 
> All the best
> AA
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