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Sometimes, while working with Python strings, we can have a problem in which we need to replace all occurrences of a substring with other.
Input : test_str = “geeksforgeeks” s1 = “geeks” s2 = “abcd”
Output : test_str = “abcdforabcd” Explanation : We replace all occurrences of s1 with s2 in test_str.
Input : test_str = “geeksforgeeks” s1 = “for” s2 = “abcd”
Output : test_str = “geeksabcdgeeks”
Approach 1
We can use inbuilt function replace present in python3 to replace all occurrences of substring.
Implementation using the inbuilt function:-
Python3
input_string = "geeksforgeeks"
s1 = "geeks"
s2 = "abcd"
input_string = input_string.replace[s1, s2]
print[input_string]
Approach 2:
Splitting the string by substring and then replacing with the new string.split[] function is used.
Python3
test_str="geeksforgeeks"
s1="geeks"
s2="abcd"
s=test_str.split[s1]
new_str=""
for i in s:
if[i==""]:
new_str+=s2
else:
new_str+=i
print[new_str]
The Time and Space Complexity for all the methods are the same:
Time Complexity: O[n]
Auxiliary Space: O[n]
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The replace[] in Python returns a copy of the string where all occurrences of a substring are replaced with another substring.
Syntax of replace[]
Syntax: string.replace[old, new, count]
Parameters:
- old – old substring you want to replace.
- new – new substring which would replace the old substring.
- count – [Optional ] the number of times you want to replace the old substring with the new substring.
Return Value : It returns a copy of the string where all occurrences of a substring are replaced with another substring.
Replace All Instances of a Single Character using replace[]
In this example, we are only replacing a single character from a given string. The Python replace[] method is case-sensitive, and therefore it performs a case-sensitive substring substitution, i.e. R in FOR is unchanged.
Python3
string = "grrks FOR grrks"
new_string = string.replace["r", "e" ]
print[string]
print[new_string]
Output :
grrks FOR grrks geeks FOR geeks
Replace All Instances of a String
Here, we replaced all the geeks with GeeksforGeeks using replace[] function.
Python3
string = "geeks for geeks \ngeeks for geeks"
print[string]
print[string.replace["geeks", "GeeksforGeeks"]]
Output :
geeks for geeks geeks for geeks GeeksforGeeks for GeeksforGeeks GeeksforGeeks for GeeksforGeeks
Replace Only a Certain Number of Instances using replace[]
In this example, we are replacing certain numbers of words. i.e. “ek” with “a” with count=3.
Python3
string = "geeks for geeks geeks geeks geeks"
print[string.replace["e", "a"]]
print[string.replace["ek", "a", 3]]
Output:
gaaks for gaaks gaaks gaaks gaaks geas for geas geas geeks geeks