How to use positive lookbehind to find only certain 3 digit numbers?

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I have this text where I want to identify only certain three digit numbers using my depart city (NYC) as the positive lookbehind expression. I don't want to include it or anything else in the result, other than the desired three digit number.

I can't simply use \d{3,} because there are other three digit numbers in this text I haven't included here which should not be in the output.

Example string:

Depart: NYC (etd 9/30), NJ (etd 10/4)
Arrive LAX
Rate: USD500, 700P

My regular expression

(?<=NYC)(\D|\S)*\d{3,}

Output

 (etd 9/30), NJ (etd 10/4) Arrive LAX Rate: USD500, 700

However, I want it to output 700 only.

I've also tried

(?<=NYC)(?<=(\D|\S)*)\d{3,}

but this doesn't output anything.

python regex
2 Answers

Using (\D|\S) matches any character except a digit, or match any non whitespace char. This will match any character, and can also be written as [\s\S] or you can let the dot match any character using (?s) or with a flag re.DOTALL

To match the first occurrence of 3 digits only without using the USD as positive lookbehind, you can capture 3 digit that are not surrounded by digits:

^[\s\S]*?(?<!\d)(\d{3})(?!\d)

The pattern matches:

  • ^ Start of string
  • [\s\S]*? Match any char including newlines, as few as possbiel
  • (?<!\d) Assert not a digit to the left
  • (\d{3}) Capture 3 digits
  • (?!\d) Assert not a digit to the right

Regex demo | Python demo

import re
 
pattern = r"^.*?(?<!\d)(\d{3})(?!\d)"
 
s = ("\"Depart: NYC (etd 9/30), NJ (etd 10/4)\n"
    "Arrive LAX\n"
    "Rate: USD500, 700P\"\n")
 
m = re.search(pattern, s, re.DOTALL)
if m:
    print (m.group(1))

To match the 700 after NYC, you can capture 3 digits preceded by a word boundary and assert no following digit

^[\s\S]*?\b(\d{3})(?!\d)

Output

500

Regex demo | Python demo

import re
 
pattern = r"^.*?\b(\d{3})(?!\d)"
s = ("\"Depart: NYC (etd 9/30), NJ (etd 10/4)\n"
    "Arrive LAX\n"
    "Rate: USD500, 700P\"\n")
 
m = re.search(pattern, s, re.DOTALL)
if m:
    print (m.group(1))

Output

700
user_54249880

You can use use

(?s)NYC.*?\b(\d{3,})

See the regex demo. Details:

  • (?s) - re.DOTALL inline modifier
  • NYC - NYC word
  • .*? - any zero or more chars as few as possible
  • \b - a word boundary
  • (\d{3,}) - Group 1: three or more digits.

See the Python demo:

import re
text = """Depart: NYC (etd 9/30), NJ (etd 10/4)
Arrive LAX
Rate: USD500, 700P"""
m = re.search(r'(?s)NYC.*?\b(\d{3,})', text)
if m:
    print(m.group(1))

# => 700
user_38329700
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