Pyhton has a method called replace in string class. It takes as input the string to be replaced and string to replace with. It is called on a string object. You can call this method in the following way to replace all 'no' with 'yes':
>>> 'no one knows how'.replace('no', 'yes') 'yes one kyesws how' >>> "chihuahua".replace("hua", "hah") 'chihahhah'
The re module in python can also be used to get the same result using regexes. re.sub(regex_to_replace, regex_to_replace_with, string) can be used to replace the substring in string.
>>> import re >>> re.sub('hua', 'hah', 'chihuahua') 'chihahhah'
re.sub is very powerful and can be used to make very subtle substitutions using regexes.