Python parsing bracketed blocks

Question

What would be the best way in Python to parse out chunks of text contained in matching brackets?

\"{ { a } { b } { { { c } } } }\"

should i

Answer 1

If you want to use a parser (lepl in this case), but still want the intermediate results rather than a final parsed list, then I think this is the kind of thing you were looking for:

>>> nested = Delayed()
>>> nested += "{" + (nested[1:,...]|Any()) + "}"
>>> split = (Drop("{") & (nested[:,...]|Any()) & Drop("}"))[:].parse
>>> split("{{a}{b}{{{c}}}}")
['{a}{b}{{{c}}}']
>>> split("{a}{b}{{{c}}}")
['a', 'b', '{{c}}']
>>> split("{{c}}")
['{c}']
>>> split("{c}")
['c']

That might look opaque at first, but it's fairly simple really :o)

nested is a recursive definition of a matcher for nested brackets (the "+" and [...] in the definition keep everything as a single string after it has been matched). Then split says match as many as possible ("[:]") of something that is surrounded by "{" ... "}" (which we discard with "Drop") and contains either a nested expression or any letter.

Finally, here's a lepl version of the "all in one" parser that gives a result in the same format as the pyparsing example above, but which (I believe) is more flexible about how spaces appear in the input:

>>> with Separator(~Space()[:]):
...     nested = Delayed()
...     nested += Drop("{") & (nested[1:] | Any()) & Drop("}") > list
...
>>> nested.parse("{{ a }{ b}{{{c}}}}")
[[['a'], ['b'], [[['c']]]]]