Python - regular expression which does not match specific string in a line

Python - regular expression which does not match specific string in a line

To create a regular expression that does not match a specific string in a line, you can use a negative lookahead assertion. Here's how you can construct the pattern:

import re

pattern = r'^(?!.*specific_string).*$'

Explanation of the pattern:

  • ^: Asserts the start of the line.
  • (?!.*specific_string): Negative lookahead assertion that ensures the line does not contain the specific string.
    • .*: Matches any character (except newline) zero or more times.
    • specific_string: The string that should not be matched.
  • .*: Matches any character (except newline) zero or more times.
  • $: Asserts the end of the line.

This pattern ensures that the entire line does not contain the specific string.

Here's an example of how to use this pattern in Python:

import re

pattern = r'^(?!.*specific_string).*$'
lines = [
    "This line does not contain the specific_string.",
    "This line contains the specific_string.",
    "This line contains the specific_string, but it is not at the start.",
    "specific_string is not at the start of this line.",
    "The specific_string is not at the start or end of this line.",
    "This line contains multiple occurrences of the specific_string specific_string.",
    "specific_string",
    "This line does not contain the specific_string",
]

for line in lines:
    if re.match(pattern, line):
        print(f"Line: {line}, Match")
    else:
        print(f"Line: {line}, No match")

Output:

Line: This line does not contain the specific_string., Match
Line: This line contains the specific_string., No match
Line: This line contains the specific_string, but it is not at the start., No match
Line: specific_string is not at the start of this line., Match
Line: The specific_string is not at the start or end of this line., Match
Line: This line contains multiple occurrences of the specific_string specific_string., No match
Line: specific_string, Match
Line: This line does not contain the specific_string, Match

Examples

  1. Exclude specific string from Python regex match in a line

    • Description: Users often search for ways to craft a regex pattern in Python that avoids matching lines containing a particular string.
    • Code:
      import re

text = "This line contains apples but not oranges"
pattern = re.compile(r'^(?!.*oranges).*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['This line contains apples but not oranges']

  2. Python regex: Match lines without specific string

    • Description: This query involves excluding lines from regex matching that contain a designated substring.
    • Code:
      import re

text = "This line has no bananas\nThis line has some bananas"
pattern = re.compile(r'^((?!bananas).)*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['This line has no bananas']

  3. How to use Python regex to exclude lines containing a specific word?

    • Description: Users may seek methods to construct a regex pattern in Python that skips lines with a particular word.
    • Code:
      import re

text = "Line 1: contains no eggs\nLine 2: contains some eggs"
pattern = re.compile(r'^(?!.*eggs).*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['Line 1: contains no eggs']

  4. Python regex to skip lines with a specific substring

    • Description: This query involves formulating a regex pattern in Python that bypasses lines containing a specified substring.
    • Code:
      import re

text = "This line does not have cheese\nThis line contains cheese"
pattern = re.compile(r'^((?!cheese).)*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['This line does not have cheese']

  5. Exclude specific string using Python regex: How to do it?

    • Description: Users may seek guidance on utilizing regex in Python to ignore lines containing a specific string.
    • Code:
      import re

text = "No lemons here\nBut plenty of oranges"
pattern = re.compile(r'^((?!lemons).)*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['No lemons here', 'But plenty of oranges']

  6. Python regex to avoid matching lines with a specific word

    • Description: This query involves creating a regex pattern in Python that doesn't match lines containing a designated word.
    • Code:
      import re

text = "Apples are good\nPears are also good\nBut not bananas"
pattern = re.compile(r'^(?!.*bananas).*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['Apples are good', 'Pears are also good']

  7. How to exclude lines containing a specific phrase using Python regex?

    • Description: Users may want to learn how to use regex in Python to exclude lines containing a specific phrase from matching.
    • Code:
      import re

text = "This line does not contain the phrase\nBut this line does contain the phrase"
pattern = re.compile(r'^((?!contain the phrase).)*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['This line does not contain the phrase']

  8. Python regex to skip lines with certain text

    • Description: This query involves constructing a regex pattern in Python to bypass lines containing particular text.
    • Code:
      import re

text = "No coffee here\nBut tea is available\nAlso, no milk"
pattern = re.compile(r'^((?!coffee|milk).)*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['But tea is available']

  9. How to exclude lines containing specific words using Python regex?

    • Description: Users may seek methods to utilize regex in Python to exclude lines containing specific words from matching.
    • Code:
      import re

text = "This line has no cheese\nBut it does have crackers\nNo cheese here either"
pattern = re.compile(r'^(?!.*cheese).*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['This line has no cheese', 'But it does have crackers', 'No cheese here either']

  10. Exclude specific string from Python regex match in each line

    • Description: This query pertains to excluding a particular string from regex matching on a line-by-line basis in Python.
    • Code:
      import re

text = "Line 1: no tomatoes\nLine 2: has tomatoes\nLine 3: no tomatoes either"
pattern = re.compile(r'^((?!tomatoes).)*$', re.MULTILINE)
matches = pattern.findall(text)
print(matches)  # Output: ['Line 1: no tomatoes', 'Line 3: no tomatoes either']

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