sscanf in Python

Question

I'm looking for an equivalent to sscanf() in Python. I want to parse /proc/net/* files, in C I could do something like this:

int matches = sscanf(
        buffer,
        "%*d: %64[0-9A-Fa-f]:%X %64[0-9A-Fa-f]:%X %*X %*X:%*X %*X:%*X %*X %*d %*d %ld %*512s\n",
        local_addr, &local_port, rem_addr, &rem_port, &inode);

I thought at first to use str.split, however it doesn't split on the given characters, but the sep string as a whole:

>>> lines = open("/proc/net/dev").readlines()
>>> for l in lines[2:]:
>>>     cols = l.split(string.whitespace + ":")
>>>     print len(cols)
1

Which should be returning 17, as explained above.

Is there a Python equivalent to sscanf (not RE), or a string splitting function in the standard library that splits on any of a range of characters that I'm not aware of?

Answer 1

You can split on a range of characters using the re module.

>>> import re
>>> r = re.compile('[ \t\n\r:]+')
>>> r.split("abc:def  ghi")
['abc', 'def', 'ghi']

Answer 2

you can turn the ":" to space, and do the split.eg

>>> f=open("/proc/net/dev")
>>> for line in f:
...     line=line.replace(":"," ").split()
...     print len(line)

no regex needed (for this case)

Answer 3

Python doesn't have an sscanf equivalent built-in, and most of the time it actually makes a whole lot more sense to parse the input by working with the string directly, using regexps, or using a parsing tool.

Probably mostly useful for translating C, people have implemented sscanf, such as in this module: http://hkn.eecs.berkeley.edu/~dyoo/python/scanf/

In this particular case if you just want to split the data based on multiple split characters, re.split is really the right tool.

Answer 4

If the separators are ':', you can split on ':', and then use x.strip() on the strings to get rid of any leading or trailing whitespace. int() will ignore the spaces.

Answer 5

You can parse with module re using named groups. It won't parse the substrings to their actual datatypes (e.g. int) but it's very convenient when parsing strings.

Given this sample line from /proc/net/tcp:

line="   0: 00000000:0203 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 335 1 c1674320 300 0 0 0"

An example mimicking your sscanf example with the variable could be:

import re
hex_digit_pattern = r"[\dA-Fa-f]"
pat = r"\d+: " + \
      r"(?P<local_addr>HEX+):(?P<local_port>HEX+) " + \
      r"(?P<rem_addr>HEX+):(?P<rem_port>HEX+) " + \
      r"HEX+ HEX+:HEX+ HEX+:HEX+ HEX+ +\d+ +\d+ " + \
      r"(?P<inode>\d+)"
pat = pat.replace("HEX", hex_digit_pattern)

values = re.search(pat, line).groupdict()

import pprint; pprint values
# prints:
# {'inode': '335',
#  'local_addr': '00000000',
#  'local_port': '0203',
#  'rem_addr': '00000000',
#  'rem_port': '0000'}

Answer 6

Upvoted orip's answer. I think it is sound advice to use re module. The Kodos application is helpful when approaching a complex regexp task with Python.

http://kodos.sourceforge.net/home.html