python - Match Everything except the string regex

Question

Data Set

Cider
631

Spruce
871

Honda
18813

Nissan
3292

Pine
10621

Walnut
10301

Code

#!/usr/bin/python
import re

text = "Cider\n631\n\nSpruce\n871Honda\n18813\n\nNissan\n3292\n\nPine\n10621\n\nWalnut\n10301\n\n"

f1 = re.findall(r"(Cider|Pine)\n(.*)",text)

print(f1)

Current Result

[('Cider', '631'), ('Pine', '10621')]

Question:

How do I change the regex from matching everything except several specified strings? ex (Honda|Nissan)

Desired Result

[('Cider', '631'), ('Spruce', '871'), ('Pine', '10621'), ('Walnut', '10301')]

Answer 1

You can exclude matching either of the names or only digits, and then match the 2 lines starting with at least a non whitespace char.

^(?!(?:Honda|Nissan|\d+)$)(\S.*)\n(.*)

The pattern matches:

• ^ Start of string
• (?! Negative lookahead, assert not directly to the right
  • (?:Honda|Nissan|\\d+)$ Match any of the alternatives at followed by asserting the end of the string
• ) Close lookahead
• (\\S.*) Capture group 1 , match a non whitespace char followed by the rest of the line
• \\n Match a newline
• (.*) Capture group 2 , match any character except a newline

Regex demo

import re

text = ("Cider\n"
            "631\n\n"
            "Spruce\n"
            "871\n\n"
            "Honda\n"
            "18813\n\n"
            "Nissan\n"
            "3292\n\n"
            "Pine\n"
            "10621\n\n"
            "Walnut\n"
            "10301")
f1 = re.findall(r"^(?!(?:Honda|Nissan|\d+)$)(\S.*)\n(.*)", text, re.MULTILINE)

print(f1)

Output

[('Cider', '631'), ('Spruce', '871'), ('Pine', '10621'), ('Walnut', '10301')]

---

If the line should start with an uppercase char AZ and the next line should consist of only digits:

^(?!Honda|Nissan)([A-Z].*)\n(\d+)$

This pattern matches:

• ^ Start of string
• (?!Honda|Nissan) Negative lookahead, assert not Honda or Nissan directly to the right
• ([AZ].*) Capture group 1 , match an uppercase char AZ followed by the rest of the line
• \\n Match a newline
• (\\d+) Capture group 2 , match 1+ digits
• $ End of string

Regex demo

Answer 2

inverse it with caret '^' symbol.

f1 = re.findall(r"(\s?^(Cider|Pine))\n(.*)",text)

Keep in mind that caret symbol (in regex) has a special meaning if it is used as a first character match which then would alternatively mean to be “does it start at the beginning of a line”.

Thats why one would insert a “non-usable character” in the beginning. I chosed an optional single space to use up that first character thereby rendering the meaning of the caret (^) symbol as NOT to mean “the beginning of the line”, but to get the desired inverse operator.