A quick reference to Python string methods - Find and Replace

September 7, 2019 · 4 minute read

Note: * represents a required parameter .

Find and Replace

find()

Parameters

string.find(substring, start, end)

substring*: the substring to be searched in the string.

start: index from which to begin the search.

end: index at which to end the search.

Return value

Returns an integer value pointing to the index of first occurrence of the substring. If the substring is not found, it returns -1.

Example

Python 3.7.4

>>> s = "I find your lack of faith disturbing"

# find 'lack' in s
>>> s.find('lack')
12

# find 'vader' in s
>>> s.find('vader')
-1

# find 'lack' in s
# begin at index 13
>>> s.find('lack', 13)
-1

# find 'lack' in s
# begin at index 11
>>> s.find('lack', 11)
12

# find 'lack' in s
# begin at index 0, end at index 2
>>> s.find('lack', 0, 2)
-1

# find 'lack' in s
# begin at index 0, end at index 13
>>> s.find('lack', 0, 13)
12

rfind()

Parameters

string.rfind(substring, start, end)

substring*: the substring to be searched in the string.

start: index from which to begin the search.

end: index at which to end the search.

Return value

Returns an integer value pointing to the highest index of the occurrence of the substring. If the substring is not found, it returns -1.

Example

Python 3.7.4

>>> s = "Bond. James Bond."

# rfind 'Bond' in s
>>> s.rfind('Bond')
12

# rfind 'Herbert' in s
>>> s.rfind('Herbert')
-1

# rfind 'Bond' in s
# begin at index 13
>>> s.rfind('Bond', 13)
-1

# rfind 'Bond' in s
# begin at index 11
>>> s.rfind('Bond', 11)
12

# rfind 'Bond' in s
# begin at index 0, end at index 5
>>> s.rfind('Bond', 0, 5)
0

# rfind 'Bond' in s
# begin at index 0, end at index 16
>>> s.rfind('Bond', 0, 16)
12

index()

Parameters

string.index(substring, start, end)

substring*: the substring to be searched in the string.

start: index from which to begin the search.

end: index at which to end the search.

Return value

Returns an integer value pointing to the index of the first occurrence of the substring. If the substring is not found, a ValueError exception is raised.

Example

Python 3.7.4

>>> s = "I find your lack of faith disturbing"

# index 'lack' in s
>>> s.index('lack')
12

# index 'vader' in s
>>> s.index('vader')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: substring not found

# index 'lack' in s
# begin at index 13
>>> s.index('lack', 13)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: substring not found

# index 'lack' in s
# begin at index 11
>>> s.index('lack', 11)
12

# index 'lack' in s
# begin at index 0, end at index 2
>>> s.index('lack', 0, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: substring not found

# index 'lack' in s
# begin at index 0, end at index 13
>>> s.index('lack', 0, 13)
12

rindex()

Parameters

string.rindex(substring, start, end)

substring*: the substring to be searched in the string.

start: index from which to begin the search.

end: index at which to end the search.

Return value

Returns an integer value pointing to the highest index of the occurrence of the substring. If the substring is not found, a ValueError exception is raised.

Example

Python 3.7.4

>>> s = "Bond. James Bond."

# rindex 'Bond' in s
>>> s.rindex('Bond')
12

# rindex 'Herbert' in s
>>> s.rindex('Herbert')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: substring not found

# rindex 'Bond' in s
# begin at index 13
>>> s.rindex('Bond', 13)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: substring not found

# rindex 'Bond' in s
# begin at index 11
>>> s.rindex('Bond', 11)
12

# rindex 'Bond' in s
# begin at index 0, end at index 5
>>> s.rindex('Bond', 0, 5)
0

# rindex 'Bond' in s
# begin at index 0, end at index 16
>>> s.rindex('Bond', 0, 16)
12

replace()

Parameters

string.replace(old, new, count)

old*: the substring to be replaced.

new*: the substring to replace old.

count: the number of instances of old you want replaced with new. If not specified, all instances of old in string will be replaced.

Return value

Returns a copy of string with all the specified instances of old replaced with new.

Example

Python 3.7.4

>>> s = "My mother thanks you. My father thanks you. My sister thanks you. And I thank you."

# replace all instances of 'thank' with 'love'
>>> s.replace('thank', 'love')
'My mother loves you. My father loves you. My sister loves you. And I love you.'

# replace the first 2 instances of 'thank' with 'love
>>> s.replace('thank', 'love', 2)
'My mother loves you. My father loves you. My sister thanks you. And I thank you.'