getting string between 2 characters in python

Question

I need to get certain words out from a string in to a new format. For example, I call the function with the input:

text2function('$sin (x)$ is an function of x')

and I need to put them into a StringFunction:

StringFunction(function, independent_variables=[vari])

where I need to get just 'sin (x)' for function and 'x' for vari. So it would look like this finally:

StringFunction('sin (x)', independent_variables=['x']

problem is, I can't seem to obtain function and vari. I have tried:

start = string.index(start_marker) + len(start_marker)
end = string.index(end_marker, start)
return string[start:end]

and

r = re.compile('$()$')
m = r.search(string)
if m:
     lyrics = m.group(1)

and

send = re.findall('$([^"]*)$',string)

all seems to seems to give me nothing.

Soorej P · Accepted Answer · 2013-05-30 11:40:17Z

30

Tweeky way!

>>> char1 = '('
>>> char2 = ')'
>>> mystr = "mystring(123234sample)"
>>> print mystr[mystr.find(char1)+1 : mystr.find(char2)]
123234sample

answered May 30, 2013 at 11:40

Soorej P

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2 Comments

M_N1 Over a year ago

Great solution! I incorporated it as a lambda for easy re-use: GetValue = lambda mystr: mystr[mystr.find(char1) + 1 : mystr.find(char2)]

DevPlayer Over a year ago

This demonstrates a good base solution but does not cover potential false-positives. If the string is not validated before hand you get bad results. my)string(123sample) or mystring(123sample\ would return strings that are likely not what you want. Using str.index() in this case would flag corrupt data (i.e. "mystring(example)")

Blender · Accepted Answer · 2013-02-23 17:28:06Z

10

$ is a special character in regex (it denotes the end of the string). You need to escape it:

>>> re.findall(r'\$(.*?)\$', '$sin (x)$ is an function of x')
['sin (x)']

answered Feb 23, 2013 at 17:28

Blender

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2 Comments

alper Over a year ago

what does r stands for do we need it?

Sean Over a year ago

raw string, so that it treats `` as an escape character

tung · Accepted Answer · 2018-12-22 06:21:12Z

7

If you want to cut a string between two identical characters (i.e, !234567890!) you can use

   line_word = line.split('!')
   print (line_word[1])

edited Dec 22, 2018 at 6:21

tung

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answered Dec 21, 2018 at 23:17

Raja Govindan

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Comments

Martijn Pieters · Accepted Answer · 2013-02-23 17:29:40Z

You need to start searching for the second character beyond start:

end = string.index(end_marker, start + 1)

because otherwise it'll find the same character at the same location again:

>>> start_marker = end_marker = '$'
>>> string = '$sin (x)$ is an function of x'
>>> start = string.index(start_marker) + len(start_marker)
>>> end = string.index(end_marker, start + 1)
>>> string[start:end]
'sin (x)'

For your regular expressions, the $ character is interpreted as an anchor, not the literal character. Escape it to match the literal $ (and look for things that are not $ instead of not ":

send = re.findall('\$([^$]*)\$', string)

which gives:

>>> import re
>>> re.findall('\$([^$]*)\$', string)
['sin (x)']

The regular expression $()$ otherwise doesn't really match anything between the parenthesis even if you did escape the $ characters.

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