how to split a string on the first instance of delimiter in python

Question

I need to split a string using python but only on the first instance of the delimiter in the string.

My code:

for line in conf.readlines():
    if re.search('jvm.args',line):
        key,value= split('=',line)
        default_args=val

The problem is line, which contains jvm.args looks like this:

'jvm.args = -Dappdynamics.com=true, -Dsomeotherparam=false,'

I want my code to split jvm.args into key and value variables incidently upon the first '='. Does re.split do this by default? If not a suggestion would be appreciated!

Since you're only interested in the the first delimiter, why not just find the match for the delimiter, with a scan of the string? Then you can just extract the two slices with line[:pos] and line[pos+1:]. — Codie CodeMonkey
– Codie CodeMonkey, Commented Jun 13, 2012 at 6:18
You don't need readlines(), stores a list in memory which is unnecessary. Just iterate over each line by simply doing this: for line in conf — jamylak
– jamylak, Commented Jun 13, 2012 at 10:40

Kenan Banks · Accepted Answer · 2012-06-13 06:22:17Z

25

This is what str.partition is for:

>>> 'jvm.args= -Dappdynamics.com=true, -Dsomeotherparam=false,'.partition('=')
('jvm.args', '=', ' -Dappdynamics.com=true, -Dsomeotherparam=false,')

From the docs:

str.partition(sep)

Split the string at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing the string itself, followed by two empty strings.

New in version 2.5.

edited Jun 13, 2012 at 6:22

answered Jun 13, 2012 at 6:17

Kenan Banks

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1 Comment

jamylak Over a year ago

@BurhanKhalid Yes, partition is optimized for this.

Burhan Khalid · Accepted Answer · 2012-06-13 06:57:59Z

13

From the split documentation

str.split([sep[, maxsplit]])

Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements)

>>> 'jvm.args= -Dappdynamics.com=true, -Dsomeotherparam=false,'.split('=',1)
['jvm.args', ' -Dappdynamics.com=true, -Dsomeotherparam=false,']

edited Jun 13, 2012 at 6:57

answered Jun 13, 2012 at 6:26

Burhan Khalid

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Comments

damned · Accepted Answer · 2012-06-13 07:34:23Z

2

I think this should work :

lineSplit = line.split("=")
key = lineSplit[0]
value = "=".join(lineSplit[1:])

As someone suggested in comments: you can just parse through string once and locate "=" , followed by splitting it from that point.

edited Jun 13, 2012 at 7:34

answered Jun 13, 2012 at 6:18

damned

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4 Comments

Ashwini Chaudhary Over a year ago

-1 value = ','.join((key,"=".join(lineSplit[1:]))) is the correct way to do it.

jamylak Over a year ago

names_with_underscores are encouraged in python.

damned Over a year ago

@jamylak i switch between java and python too frequently and this is the pattern I follow :) Thanks for suggestion though !

damned Over a year ago

@AshwiniChaudhary The question says "I need to split a string using python but only on the first instance of the delimter in the string." and my code does the same. What you wrote, gives more explicit separation of arguments though.

Codie CodeMonkey · Accepted Answer · 2012-06-13 06:56:48Z

1

I guess I'll turn my comment into (untested) code because it might be useful at a lower level than str.partition(). For example, for a more complicated delimiter requiring a regular expression, you could use re.match() to find pos. But Triptych's suggestion got my vote.

Here you go:

pos = -1
for i, ch in enumerate(line):
    if ch == '=':
        pos = i
        break
if pos < 0: raise myException()

key = line[:pos]
value = line[pos+1:]

edited Jun 13, 2012 at 6:56

answered Jun 13, 2012 at 6:24

Codie CodeMonkey

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Comments

Tim · Accepted Answer · 2012-06-13 06:49:46Z

I'd skip using regular expressions completely, for a simple string comparison they are not really required.

The example code uses an inline method to yield key,value tuples that the dict builtin uses to generate a dictionary (I've not bothered with the file iteration code, your example is correct there):

line="jvm.args= -Dappdynamics.com=true, -Dsomeotherparam=false, "

# Detect a line that starts with jvm.args
if line.strip().startswith('jvm.args'):
    # Only interested in the args
    _, _, args = line.partition('=')

    # Method that will yield a key, value tuple if item can be converted
    def key_value_iter(args):
        for arg in args:
            try:
                key, value = arg.split('=')
                # Yield tuple removing the -d prefix from the key
                yield key.strip()[2:], value
            except:
                # A bad or empty value, just ignore these
                pass

    # Create a dict based on the yielded key, values
    args = dict(key_value_iter(args.split(',')))

print args will return:

{'appdynamics.com': 'true', 'someotherparam': 'false'}

I assume this is what you are actually after ;)

Community · Accepted Answer · 2017-05-23 10:31:29Z

0

As suggested in your previous question, ConfigParser is the most straightforward way:

import ConfigParser

from io import StringIO

conf = u"""
[options]
foo=bar
jvm.args= -Dappdynamics.com=true, -Dsomeotherparam=false, 
"""

config = ConfigParser.ConfigParser()
config.readfp(StringIO(conf))
print config.get('options', 'jvm.args')

edited May 23, 2017 at 10:31

CommunityBot

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answered Jun 13, 2012 at 7:04

georg

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