Check if String Present in Another String in Python

In Python if you want to check if a given String is present in another String then you have following options-

Use Python membership operators ‘in’ and ‘not in’. See example.
Using find() method to check if string contains another string. See example.
Using index() method to get the index of the substring with in the String. See example.

Python membership operators - in and not in

If you want to check if a String is member of another String then you can use ‘in’ and ‘not in’ membership operators.

‘in’ operator- Returns true if the string is part of another string otherwise false.
‘not in’ operator- Returns true if the string is not part of another string otherwise false.

Python in operator example

def check_membesrship(str1, str2):
  if str2 in str1:
    print(str2, 'found in String')
  else:
    print(str2, 'not found in String')

str1 = "This is Python"
str2 = "Python"
check_membesrship(str1, str2)
#another call
check_membesrship(str1, 'That')

Output

Python found in String
That not found in String

Python not in operator example

def check_membesrship(str1, str2):
  if str2 not in str1:
    print(str2, 'not found in String')
  else:
    print(str2, 'found in String')

str1 = "This is Python"
str2 = "Python"
check_membesrship(str1, 'That')
#another call
check_membesrship(str1, str2)

Output

That not found in String
Python found in String

Using find() method to check if substring exists in string

Using find() method in Python you can check if substring is part of the string or not. If found, this method returns the location of the first occurrence of the substring otherwise -1 is returned.

Python find() method example

def check_membesrship(str, substr):
  loc = str.find(substr)
  if loc == -1:
    print(substr, 'not found in String')
  else:
    print(substr, 'found in String at index', loc)


str1 = "This is Python"
str2 = "Python"
check_membesrship(str1, str2)
#another call
check_membesrship(str1, 'That')

Output

Python found in String at index 8
That not found in String

Using index() method to check if substring exists in string

Using index() method in Python you can check if substring is part of the string or not. This method is similar to find() and returns the location of the first occurrence of the substring if found. If not found then index() method raises ‘ValueError’ exception that's where it differs from find().

Python index() method example

def check_membesrship(str, substr):
  # Catch ValueError exception
  try:
    loc = str.index(substr)
  except ValueError:
    print(substr, 'not found in String')
  else:
    print(substr, 'found in String at index', loc)


str1 = "This is Python"
str2 = "Python"
check_membesrship(str1, str2)
#another call
check_membesrship(str1, 'That')

Output

Python found in String at index 8
That not found in String

That's all for this topic Check if String Present in Another String in Python. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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Sunday, February 9, 2020