Check if a string does NOT contain substring in Python

I will introduce a new topic to you today: Check if a string does NOT contain a substring in Python. This is a fundamental topic; to do this, I will use the functions available in Python such as str.index(), str.find()…Details are in the article below.

Check if a string does NOT contain substring in Python.

Use the Authentication operator

Example:

originalStr = 'Hello! Visit LearnshareIt to read great articles on programming languages.'

subStr = 'LearnshareIt'

# Use the Authentication operator.
if subStr not in originalStr:
    print('The substring does not appear in the original string.')
else:
    print('The substring appears in the original string.')

Output:

The substring appears in the original string.

Use the str.index() function

Syntax:

str.index(str, start, end)

Parameters:

  • str: Specifies the search string.
  • start: The starting index. The default is 0.
  • end: End index. The default is the string length.

Example:

originalStr = 'Hello! Visit LearnshareIt to read great articles on programming languages.'
subStr = 'LearnshareIt'

try:
    # Use the str.index() to check for occurrence of substring.
    originalStr.index(subStr) != -1
    print('The substring appears in the original string.')
except ValueError:
    print('The substring does not appear in the original string.')

Output:

The substring appears in the original string.

Note: The str.index() function will return an exception if the substring is not found.

Use the str.find() method

Like the str.index() function, you can use the str.find() function with the same function and parameters.

Syntax:

str.find(str, start, end)

Parameters:

  • str: Specifies the search string.
  • start: The starting index. The default is 0.
  • end: End index. The default is the string length.

Example:

originalStr = 'Hello! Visit LearnshareIt to read great articles on programming languages.'
subStr = 'LearnshareIt'

# Use the str.find() to check for occurrence of substring.
if originalStr.find(subStr) != -1:
   print('The substring appears in the original string.')
else:
   print('The substring does not appear in the original string.')

Output:

The substring appears in the original string.

Use the re.search() function

Syntax:

re.search(pattern, str)

Parameters:

  • pattern: is RegEx.
  • str: search string.

Example:

import re

originalStr = 'Hello! Visit LearnshareIt to read great articles on programming languages.'
subStr = 'LearnshareIt'

# Use the re.search() to check for occurrence of substring.
if re.search(subStr, originalStr):
   print('The substring appears in the original string.')
else:
   print('The substring does not appear in the original string.')

Output:

The substring appears in the original string.

Summary

The article Check if a string does NOT contain substring in Python is probably solved. You can use one of the four methods above because they are entirely built-in functions in Python. If you have any questions or have a more creative way, I hope you will share it with everyone by commenting below. Thank you for reading my article.

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