String parsing with Python

Question

I can't seem to find any docs on the parse() method for strings. Is there a good reference? I want to parse the following:

frame 0 rows {3 2 3 3 3 3 2 3 2 3 3 3 2 3 2 3 4 3 3 4 3 2 2 3 3 3 2 2 2 2 3 3 3 2 3 2 3 3 3 3 4 3 4 3 3 3 3 4 3 2 3 3 3 3 2 2 2 4 4 3 3 3 3 3 4 4 4 3 2 4 3 4 3 3 3 4 3 3 4 3 3 4 4 3 3 3 4 4 3 4 3 3 3 3 3 4} columns {2 3 2 3 3 3 4 3 3 2 3 2 2 2 3 2 3 3 2 2 2 3 3 3 3 2 3 3 3 2 3 3 2 2 2 3 3 4 3 3 3 3 3 3 3 3 2 3 3 3 3 4 3 2 3 2 3 3 3 3 3 2 2 3 3 3 3 2 3 3 3 3 3 3 3 3 3 4 3 3 3 3 3 4 3 3 4 3 4 4 4 3 4 4 4 4 4 4 3 3 4 4 3 4 4 4 4 3 3 3 4 4 3 4 4 3 3 4 3 5 5 5 5 4 5 4 4 4}

into two lists of int.

That's not what string.parse() is designed to be used for (it's used internally as part of string.format()). Try taking a look at the re regular expressions library instead. — Amber
– Amber, Commented Mar 14, 2011 at 2:09

A. Jesse Jiryu Davis · Accepted Answer · 2011-03-14 02:09:31Z

5

Python strings' parse() won't help you here (it has a very obscure use). In this case, I'd do it the obvious way: With regexes! If 's' is your string above,

import re
lists = [
    [int(i) for i in match.split()]
    for match in re.findall(r'{(.*?)}', s)
]

print lists

answered Mar 14, 2011 at 2:09

A. Jesse Jiryu Davis

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Utku Zihnioglu · Accepted Answer · 2011-03-14 02:08:43Z

>>> a="frame 0 rows {3 2 3 3 3 3 2 3 2 3 3 3 2 3 2 3 4 3 3 4 3 2 2 3 3 3 2 2 2 2 3 3 3 2 3 2 3 3 3 3 4 3 4 3 3 3 3 4 3 2 3 3 3 3 2 2 2 4 4 3 3 3 3 3 4 4 4 3 2 4 3 4 3 3 3 4 3 3 4 3 3 4 4 3 3 3 4 4 3 4 3 3 3 3 3 4} columns {2 3 2 3 3 3 4 3 3 2 3 2 2 2 3 2 3 3 2 2 2 3 3 3 3 2 3 3 3 2 3 3 2 2 2 3 3 4 3 3 3 3 3 3 3 3 2 3 3 3 3 4 3 2 3 2 3 3 3 3 3 2 2 3 3 3 3 2 3 3 3 3 3 3 3 3 3 4 3 3 3 3 3 4 3 3 4 3 4 4 4 3 4 4 4 4 4 4 3 3 4 4 3 4 4 4 4 3 3 3 4 4 3 4 4 3 3 4 3 5 5 5 5 4 5 4 4 4}"

>>> import ast
>>> import re
>>> for match in re.finditer("\{([\d ]+)\}",a):
    integers=match.groups()[0]
    l=ast.literal_eval(integers.replace(" ",","))
    print l


(3, 2, 3, 3, 3, 3, 2, 3, 2, 3, 3, 3, 2, 3, 2, 3, 4, 3, 3, 4, 3, 2, 2, 3, 3, 3, 2, 2, 2, 2, 3, 3, 3, 2, 3, 2, 3, 3, 3, 3, 4, 3, 4, 3, 3, 3, 3, 4, 3, 2, 3, 3, 3, 3, 2, 2, 2, 4, 4, 3, 3, 3, 3, 3, 4, 4, 4, 3, 2, 4, 3, 4, 3, 3, 3, 4, 3, 3, 4, 3, 3, 4, 4, 3, 3, 3, 4, 4, 3, 4, 3, 3, 3, 3, 3, 4)
(2, 3, 2, 3, 3, 3, 4, 3, 3, 2, 3, 2, 2, 2, 3, 2, 3, 3, 2, 2, 2, 3, 3, 3, 3, 2, 3, 3, 3, 2, 3, 3, 2, 2, 2, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 3, 2, 3, 3, 3, 3, 4, 3, 2, 3, 2, 3, 3, 3, 3, 3, 2, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 3, 3, 3, 4, 3, 3, 4, 3, 4, 4, 4, 3, 4, 4, 4, 4, 4, 4, 3, 3, 4, 4, 3, 4, 4, 4, 4, 3, 3, 3, 4, 4, 3, 4, 4, 3, 3, 4, 3, 5, 5, 5, 5, 4, 5, 4, 4, 4)

I have never heard of a parse method to actually parses the string in the way you ask. However, parsing that string is not that hard. Here is how to do it.

@Senthil: There is no good reason to use it in this particular case. Just calling int() like in Jesse's answer is probably more efficient and right way to do it.
@funktu: Thanks for the answer anyway as I am still not familiar with ast, and it's good to some examples of its use.

PaulMcG · Accepted Answer · 2011-03-14 04:32:36Z

For such nicely structured data, pyparsing may be more than you need, but it makes for a good tutorial example:

from pyparsing import *

s = "frame 0 rows {3 2 3 3 3 3 2 3 2 3 3 3 2 3 2 3 4 3 3 4 3 2 2 3 3 3 2 2 2 2 3 3 3 2 3 2 3 3 3 3 4 3 4 3 3 3 3 4 3 2 3 3 3 3 2 2 2 4 4 3 3 3 3 3 4 4 4 3 2 4 3 4 3 3 3 4 3 3 4 3 3 4 4 3 3 3 4 4 3 4 3 3 3 3 3 4} columns {2 3 2 3 3 3 4 3 3 2 3 2 2 2 3 2 3 3 2 2 2 3 3 3 3 2 3 3 3 2 3 3 2 2 2 3 3 4 3 3 3 3 3 3 3 3 2 3 3 3 3 4 3 2 3 2 3 3 3 3 3 2 2 3 3 3 3 2 3 3 3 3 3 3 3 3 3 4 3 3 3 3 3 4 3 3 4 3 4 4 4 3 4 4 4 4 4 4 3 3 4 4 3 4 4 4 4 3 3 3 4 4 3 4 4 3 3 4 3 5 5 5 5 4 5 4 4 4}"

LBRACE,RBRACE = map(Suppress,"{}")
integer = Word(nums).setParseAction(lambda t:int(t[0]))

line = ("frame" + integer("frame") + 
        "rows" + LBRACE + ZeroOrMore(integer)("rows") + RBRACE + 
        "columns" + LBRACE + ZeroOrMore(integer)("columns") + RBRACE )

data = line.parseString(s)
print data.frame
print data.rows[:10]
print data.columns[:10]

prints:

0
[3, 2, 3, 3, 3, 3, 2, 3, 2, 3]
[2, 3, 2, 3, 3, 3, 4, 3, 3, 2]

Tom · Accepted Answer · 2011-03-14 02:08:03Z

0

type pydoc -p 5000 into the command line then got to http://localhost:5000/string.html#Formatter-parse

answered Mar 14, 2011 at 2:08

Tom

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Comments

dting · Accepted Answer · 2011-03-14 02:22:55Z

m_string = "frame 0 rows {3 2 3 3 3 3 2 3 2 3 3 3 2 3 2 3 4 3 3 4 3 2 2 3 3 3 2 2 2 2 3 3 3 2 3 2 3 3 3 3 4 3 4 3 3 3 3 4 3 2 3 3 3 3 2 2 2 4 4 3 3 3 3 3 4 4 4 3 2 4 3 4 3 3 3 4 3 3 4 3 3 4 4 3 3 3 4 4 3 4 3 3 3 3 3 4} columns {2 3 2 3 3 3 4 3 3 2 3 2 2 2 3 2 3 3 2 2 2 3 3 3 3 2 3 3 3 2 3 3 2 2 2 3 3 4 3 3 3 3 3 3 3 3 2 3 3 3 3 4 3 2 3 2 3 3 3 3 3 2 2 3 3 3 3 2 3 3 3 3 3 3 3 3 3 4 3 3 3 3 3 4 3 3 4 3 4 4 4 3 4 4 4 4 4 4 3 3 4 4 3 4 4 4 4 3 3 3 4 4 3 4 4 3 3 4 3 5 5 5 5 4 5 4 4 4}"

import re

print [[ int(i) for i in  x.split(" ")] for x in [ match for match in re.findall("\{([\d ]+)\}", m_string)] ]

results in:

[[3, 2, 3, 3, 3, 3, 2, 3, 2, 3, 3, 3, 2, 3, 2, 3, 4, 3, 3, 4, 3, 2, 2, 3, 3, 3, 2, 2, 2, 2, 3, 3, 3, 2, 3, 2, 3, 3, 3, 3, 4, 3, 4, 3, 3, 3, 3, 4, 3, 2, 3, 3, 3, 3, 2, 2, 2, 4, 4, 3, 3, 3, 3, 3, 4, 4, 4, 3, 2, 4, 3, 4, 3, 3, 3, 4, 3, 3, 4, 3, 3, 4, 4, 3, 3, 3, 4, 4, 3, 4, 3, 3, 3, 3, 3, 4], [2, 3, 2, 3, 3, 3, 4, 3, 3, 2, 3, 2, 2, 2, 3, 2, 3, 3, 2, 2, 2, 3, 3, 3, 3, 2, 3, 3, 3, 2, 3, 3, 2, 2, 2, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 3, 2, 3, 3, 3, 3, 4, 3, 2, 3, 2, 3, 3, 3, 3, 3, 2, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 3, 3, 3, 4, 3, 3, 4, 3, 4, 4, 4, 3, 4, 4, 4, 4, 4, 4, 3, 3, 4, 4, 3, 4, 4, 4, 4, 3, 3, 3, 4, 4, 3, 4, 4, 3, 3, 4, 3, 5, 5, 5, 5, 4, 5, 4, 4, 4]]

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