Question

I have to parse an input string in python and extract certain parts from it.

the format of the string is

(xx,yyy,(aa,bb,...)) // Inner parenthesis can hold one or more characters in it

I want a function to return xx, yyyy and a list containing aa, bb … etc

I can ofcourse do it by trying to split of the parenthesis and stuff but I want to know if there a proper pythonic way of extracting such info from a string

I have this code which works, but is there a better way to do it (without regex)

def processInput(inputStr):
    value = inputStr.strip()[1:-1]
    parts = value.split(',', 2)
    return parts[0], parts[1], (parts[2].strip()[1:-1]).split(',')

Answer 1

If you’re allergic to REs, you could use pyparsing:

>>> import pyparsing as p
>>> ope, clo, com = map(p.Suppress, '(),')
>>> w = p.Word(p.alphas)
>>> s = ope + w + com + w + com + ope + p.delimitedList(w) + clo + clo
>>> x = '(xx,yyy,(aa,bb,cc))'
>>> list(s.parseString(x))
['xx', 'yyy', 'aa', 'bb', 'cc']

pyparsing also makes it easy to control the exact form of results (e.g. by grouping the last 3 items into their own sublist), if you want. But I think the nicest aspect is how natural (depending on how much space you want to devote to it) you can make the “grammar specification” read: an open paren, a word, a comma, a word, a comma, an open paren, a delimited list of words, two closed parentheses (if you find the assignment to s above not so easy to read, I guess it’s my fault for not choosing longer identifiers;-).