Find multiple elements in string in Python

Question

my problem is that I need to find multiple elements in one string.

For example I got one string that looks like this:

line = if ((var.equals("INPUT")) || (var.equals("OUTPUT"))

and then i got this code to find everything between ' (" ' and ' ") '

char1 = '("'
char2 = '")'


add = line[line.find(char1)+2 : line.find(char2)]
list.append(add)

The current result is just:

['INPUT']

but I need the result to look like this:

['INPUT','OUTPUT', ...]

after it got the first match it stopped searching for other matches, but I need to find everything in that string that matches this search.

I also need to append every single match to the list.

score 5 · Accepted Answer · answered Nov 23 '18 at 08:42

5

The simplest:

>>> import re
>>> s = """line = if ((var.equals("INPUT")) || (var.equals("OUTPUT"))"""
>>> r = re.compile(r'\("(.*?)"\)')
>>> r.findall(s)
['INPUT', 'OUTPUT']

The trick is to use .*? which is a non-greedy *.

answered Nov 23 '18 at 08:42

Samuel GIFFARD

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1

This is the way to do it. +1 – Ma0 Nov 23 '18 at 08:44
Thanks, im using this now. – M4I3X Nov 23 '18 at 09:06
I got one more thing, how can i get the result of findall into a variable? If i try `result = r.findall(s)` i get this error `TypeError: expected string or bytes-like object` – M4I3X Nov 23 '18 at 09:15
Your code should work. Looks more like an encoding issue. You're Python 2 or Python 3? Check the type of your input. With something like `print(my_input.__class__)` – Samuel GIFFARD Nov 23 '18 at 09:22
I solved it, i was reading lines from a file but forgot to assign a variable to it^^ – M4I3X Nov 23 '18 at 09:32

Raniz · Answer 2 · 2018-11-23T08:48:36.447

1

You should look into regular expressions because that's a perfect fit for what you're trying to achieve.

Let's examine a regular expression that does what you want:

import re
regex = re.compile(r'\("([^"]+)"\)')

It matches the string (" then captures anything that isn't a quotation mark and then matches ") at the end.

By using it with findall you will get all the captured groups:

In [1]: import re

In [2]: regex = re.compile(r'\("([^"]+)"\)')

In [3]: line = 'if ((var.equals("INPUT")) || (var.equals("OUTPUT"))'

In [4]: regex.findall(line)
Out[4]: ['INPUT', 'OUTPUT']

edited Nov 23 '18 at 08:48

answered Nov 23 '18 at 08:46

Raniz

10,048
1
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61

NB: Will not work if there's a `"` in the string that he wants to find. Non-greedy star operator `*?` is the clean way to go there. – Samuel GIFFARD Nov 23 '18 at 08:48
That was intentional though – Raniz Nov 23 '18 at 08:49
Regular experssions are not generally a good fit for [brackets matching](https://stackoverflow.com/a/546457/4050925). For this particular task it works, but it can break easily (or get messy) if doing something slightly more complicated. Just a heads up to the OP – Robin Nemeth Nov 23 '18 at 09:24

score 0 · Answer 3 · answered Nov 23 '18 at 08:41

0

If you don't want to use regex, this will help you.

line = 'if ((var.equals("INPUT")) || (var.equals("OUTPUT"))'
char1 = '("'
char2 = '")'


add = line[line.find(char1)+2 : line.find(char2)]
list.append(add)
line1=line[line.find(char2)+1:]
add = line1[line1.find(char1)+2 : line1.find(char2)]
list.append(add)
print(list)

just add those 3 lines in your code, and you're done

answered Nov 23 '18 at 08:41

Sandesh34

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how that method will help if will be more than two `("...")` in line? – Andrey Suglobov Nov 23 '18 at 08:57

score 0 · Answer 4 · answered Nov 23 '18 at 08:47

if I understand you correct, than something like that is help you:

line = 'line = if ((var.equals("INPUT")) || (var.equals("OUTPUT"))'
items = []
start = 0
end = 0
c = 0;
while c < len(line):
    if line[c] == '(' and line[c + 1] == '"':
        start = c + 2
    if line[c] == '"' and line[c + 1] == ')':
        end = c
    if start and end:
        items.append(line[start:end])
        start = end = None
    c += 1

print(items)    # ['INPUT', 'OUTPUT']

Find multiple elements in string in Python

4 Answers4