extracting unknown substring from a string in python

Question

I have the following string:

HTTP/1.1 200 OK
CACHE-CONTROL: max-age=100
EXT:
LOCATION: string to be extracted followed by a \n
SERVER: FreeRTOS/6.0.5, UPnP/1.0, IpBridge/0.1
ST: urn:schemas-upnp-org:device:basic:1
USN: uuid:2f402f80-da50-11e1-9b23-0017881892ca

I want to extract whatever follows LOCATION: until the new line.

I can't do substring in string method as whatever follows 'LOCATION: ` may change.

I tried making this string into a dictionary and then retrieve the value of 'LOCATION' key. But this seems like a waste of memory and processing time. As the dictionary is useless to me apart from that value. Also the dictionary may grow geatlt in size if the string is too large

Is there any other way to extract whatever follows 'LOCATION: ` until the '\n' ??

you can use regular expression for this task. https://docs.python.org/2/howto/regex.html — Pavan Gupta, Jun 05 '14 at 06:46

Sayan Chowdhury · Answer 1 · 2014-06-05T06:56:54.667

4

You extract the string using regular expressions

>>> import re
>>> string = """HTTP/1.1 200 OK
... CACHE-CONTROL: max-age=100
... EXT:
... LOCATION: http://129.94.5.95:80/description.xml
... SERVER: FreeRTOS/6.0.5, UPnP/1.0, IpBridge/0.1
... ST: urn:schemas-upnp-org:device:basic:1
... USN: uuid:2f402f80-da50-11e1-9b23-0017881892ca
... """
>>> regex = re.compile('LOCATION: (.*?)\n')
>>> m = regex.search(string)
>>> if m:
...     print m.group(1)
http://129.94.5.95:80/description.xml

edited Jun 05 '14 at 06:56

answered Jun 05 '14 at 06:45

Sayan Chowdhury

419
4
13

is regex variable a string in this ? – sukhvir Jun 05 '14 at 06:46
No, but `regex.group(1)` is a string. – Adam Jun 05 '14 at 06:48
2

you probably want to split the search and group extraction up, so that you can test for `None` in case there is no match. – Adam Jun 05 '14 at 06:48
Yes, as @Adam said `regex.group(1)` is the string. – Sayan Chowdhury Jun 05 '14 at 06:53
your answer saved my day, thanks – thahgr May 15 '20 at 11:25

thefourtheye · Answer 2 · 2014-06-05T11:52:41.353

2

You can split the lines with splitlines and then split the individual lines based on :, to convert them to a dictionary, like this

d = dict(item.split(": ", 1) for item in data.splitlines() if ": " in item)
print d["LOCATION"]
# http://129.94.5.95:80/description.xml

To have the keys converted to lowercase letters, you can reconstruct the dictionary like this

d = dict(item.split(": ", 1) for item in data.splitlines() if ": " in item)
d = {key.lower():d[key] for key in d}
print d["location"]

edited Jun 05 '14 at 11:52

answered Jun 05 '14 at 06:42

thefourtheye

233,700
52
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Downvoter, please let me know how this post can be improved. – thefourtheye Jun 05 '14 at 06:54
heck, I liked your solution so much I deleted my RE-based one. – Adam Jun 05 '14 at 06:57
Is it possible to lowercase the keys of this dictionary without affecting the values ? – sukhvir Jun 05 '14 at 11:35
@sukhvir Only the keys? – thefourtheye Jun 05 '14 at 11:49

Louis · Answer 3 · 2014-06-05T06:51:01.057

2

string.index(character) is what you need :

 mystr="HTTP/1.1 200 OK\nCACHE-CONTROL: max-age=100\nEXT:\nLOCATION: string to be extracted followed by a \nSERVER: FreeRTOS/6.0.5, UPnP/1.0, IpBridge/0.1\nST: urn:schemas-upnp-org:device:basic:1\nUSN: uuid:2f402f80-da50-11e1-9b23-0017881892ca"
search = "LOCATION"
start = mystr.index(search)+len(search)
stop = mystr.index("\n", start)
print mystr [ start : stop ]

edited Jun 05 '14 at 06:51

answered Jun 05 '14 at 06:42

Louis

2,854
2
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read my update, sorry for misspelling my first answer. – Louis Jun 05 '14 at 06:52
This is incorrect. It yields the string ": string to be extracted followed by a ". – Adam Jun 05 '14 at 21:01
Adam : well, that's precisely what is in the string, read the question ! – Louis Jun 06 '14 at 12:11

Ankur Ankan · Accepted Answer · 2014-06-07T07:01:50.567

2

You could split the whole string on newline. And then check each line if they start with LOCATION. If it does print the remaining line.

string = """HTTP/1.1 200 OK
CACHE-CONTROL: max-age=100
EXT:
LOCATION: http://129.94.5.95:80/description.xml
SERVER: FreeRTOS/6.0.5, UPnP/1.0, IpBridge/0.1
ST: urn:schemas-upnp-org:device:basic:1
USN: uuid:2f402f80-da50-11e1-9b23-0017881892ca"""



 for line in string.split('\n'):
     if line.startswith('LOCATION'):
         print(line[10:])
         break

Out: http://129.94.5.95:80/description.xml

edited Jun 07 '14 at 07:01

answered Jun 05 '14 at 06:47

Ankur Ankan

2,953
2
23
38

1

Several reasons: *Zero* explanation for the code, shadowing the `str` builtin type in an example that people might copy and paste, hard-coding the value `10`, bad indentation. As it stands, @thefourtheye's solution is much better and solves the general case. – Lukas Graf Jun 05 '14 at 07:11

extracting unknown substring from a string in python

4 Answers4