How to find substring in Python string

Question

I have an list of strings as follows:

strings = [
  "On monday we had total=5 cars",
  "On tuesday we had total = 15 cars",
  "On wensdsday we are going to have total=9 or maybe less cars"
]

I want to be able to find and replace substring from those strings.

I can find and replace it as follows (If I have string with which I want to replace):

new_total = "total = 20"
for str in strings:
  new_string = re.sub(r"total\s?=\s?5", "{}".format(new_total), str)
  print(new_string)

In this case it matches only total=5. This is not what I want.

I want first to extract the total = <value> from a sentence, no matter if it has blank spaces before or after = sign, and then insert the extracted value into the other sentences

Thus something as follows:

some_sentence = "We will use this sentence to get total=20 of cars."
new_total = "????" // it needs to get total=20 
for str in strings:
  // Here I want to replace `total=<value>` or `total = <value>` in every str with new_total
  new_string = "????"
  print(new_string)

The output should be:

"On monday we had total=20 cars",
"On tuesday we had total=20 cars",
"On wensdsday we are going to have total=20 or maybe less cars"

Any idea how can I do that?

It would help if you could explicitly state what you want to do: "I want to add spaces around the =-sign in total = XXX". Makes your question easier to understand with a fraction of the text. — Aran-Fey
– Aran-Fey, Commented Mar 19, 2018 at 9:26
@Aran-Fey I want to get substring from a sentence some_sentence = "We will use this sentence to get total=20 of cars." no matter if it has blank spaces before and after equal sign. And then add it in every string in list of string instead of total = <value> or total=<value> — Boky
– Boky, Commented Mar 19, 2018 at 9:33
Oh, so you first want to extract the total = XXX from a sentence, and then insert the extracted value into the other sentences? I get it now. But your question is horribly unclear IMO. You should try to clarify it. (As in, in the question itself, not in the comments.) — Aran-Fey
– Aran-Fey, Commented Mar 19, 2018 at 9:35

Mike Scotty · Accepted Answer · 2018-03-19 09:35:27Z

1

You were almost there. Instead of your hardcoded 5 use \d+ in the regex:

import re

strings = [
  "On monday we had total=5 cars",
  "On thursday we had total = 15 cars",
  "On wendesday we are going to have total=9 or maybe less cars"
]

new_total = "total = 20"
for s in strings:
  new_string = re.sub(r"total\s?=\s?\d+", "{}".format(new_total), s)
  print(new_string)

# to extract the information you can use:
p = re.compile(r"(total\s?=\s?\d+)")
for s in strings:
  print( p.findall(s) )

Output:

On monday we had total = 20 cars
On thursday we had total = 20 cars
On wendesday we are going to have total = 20 or maybe less cars
['total=5']
['total = 15']
['total=9']

If you are sure you will have a match, you could also use p.search(s).group(0) (which will return the string instead of a list) instead of p.findall(s).

edited Mar 19, 2018 at 9:35

answered Mar 19, 2018 at 9:26

Mike Scotty

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2 Comments

Boky Over a year ago

Ok. But I want to get total=<value> from a sentence. some_sentence = "We will use this sentence to get total=20 of cars.". How can I get total=20 from some_sentence?

Mike Scotty Over a year ago

@Aran-Fey the .* part can be usefull if you want the parts before and after the match to be accessible in separate groups. But I removed them, because they are really not neccessary here.

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