Replace A Character Or Substring In A Python String

string = 'the quick brown fox'
new_string = string.replace('quick', 'slow')

print(new_string)

Outputs:

the slow brown fox

If you only want to replace a certain number, add a third parameter with the count.

string = 'a1 a2 a3 a4 a5 a6'
new_string = string.replace('a', 'B', 3)

print(new_string)

Outputs:

B1 B2 B3 a4 a5 a6