How do I extract a certain part of a string in Python?

Question

I was wondering how I would extract a certain part of a string in Python.

So, let's say I have a list. (EXAMPLE)

1 || awdawd@awdawd.com || awlkdjawldkjalwdkda
2 || aawdawd@awd.com || awdadwawdawdawdawd

I know I could use indexing and take the last 10 or so characters from each line, but that wouldn't work if they're different lengths. And it wouldn't work at all for the email.

I'm thinking regular expressions, but once I find the portion of the string, how would I copy just that part of the string and append it to, say, a list.

The regular expression is simple for the email, but not so simple for the string after the '||'. So how would I do that? I'm having trouble getting my head around it. Maybe search for || and get everything after it? But then there's two '||'.

Any help is appreciated.

What part of the string do you want to extract? Do you want to split based on `||` and take the third element? — Yannick Meeus, Feb 17 '15 at 11:13
Is there always an email after the first `||`? If so just look for the `||` that isn't followed by an email or preceded by the number. — Aleksander Lidtke, Feb 17 '15 at 11:14
Basically, I want to parse a list that looks like the following into: email:finalstring — Awn, Feb 17 '15 at 11:15
Okay, @Aleksander, but how would I actually take that part of the string out? — Awn, Feb 17 '15 at 11:16
possible duplicate of [Extract portions of text if Regex in Python](http://stackoverflow.com/questions/11684529/extract-portions-of-text-if-regex-in-python) — NeronLeVelu, Feb 17 '15 at 16:08

score 3 · Answer 1 · answered Feb 17 '15 at 11:15

3

Get the reverse index after splitting by ||:

>>> L = ["|| awdawd@awdawd.com || awlkdjawldkjalwdkda", "|| aawdawd@awd.com || awdadwawdawdawdawd"]
>>> for x in L:
...     print x.split('||')[-1].strip()
... 
awlkdjawldkjalwdkda
awdadwawdawdawdawd

answered Feb 17 '15 at 11:15

TerryA

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That seems to work. Hmm, what does [-1] do? Read from the back of the string? – Awn Feb 17 '15 at 11:17
@Aurora Pretty much: http://stackoverflow.com/questions/509211/explain-pythons-slice-notation – TerryA Feb 17 '15 at 12:26

score 2 · Accepted Answer · answered Feb 17 '15 at 11:27

Firstly, if you know the exact format of strings you may use split() function. For example

>>> string1 = "1 || awdawd@awdawd.com || awlkdjawldkjalwdkda"
>>> list1 = string1.split("||")
>>> list1
['1 ', ' awdawd@awdawd.com ', ' awlkdjawldkjalwdkda']
>>> list1[1].strip()
'awdawd@awdawd.com'

If you split a given string using substring "||" you'll receive a list of three elements. E-mail will be the second one, and the strip() function will give you the email without whitespace characters.

If you don't know exact structure of strings, but you know what substrings you want to extract you can use regular expressions, there are quite a few recipes for it, here is one for emails.

score 1 · Answer 3 · answered Feb 17 '15 at 11:17

1

I think you want the first part. This splits the input according to ||, and then print the stripped content of index 1.

>>> s = '1 || awdawd@awdawd.com || awlkdjawldkjalwdkda'
>>> s.split('||')[1].strip()
'awdawd@awdawd.com'
>>> L = ["|| awdawd@awdawd.com || awlkdjawldkjalwdkda", "|| aawdawd@awd.com || awdadwawdawdawdawd"]
>>> for x in L:
        print(x.split('||')[1].strip())


awdawd@awdawd.com
aawdawd@awd.com

answered Feb 17 '15 at 11:17

Avinash Raj

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Ahh, I see. You just answered my question on the first reply too. Thank you. – Awn Feb 17 '15 at 11:19

score 1 · Answer 4 · answered Feb 17 '15 at 11:21

1

I think str.split('||') is there for exactly this use case.

To remove remaining whitespace, use str.strip() on the returned array elements.

answered Feb 17 '15 at 11:21

deyhle

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How do I extract a certain part of a string in Python?

4 Answers4