>>> sentence.count('e',7)

Replaces all occurences of a given substring with another substring. Can be optionally provided a third argument to limit the number of replacements. Returns a new string.

>>> text="Hello, world!"

>>> text.replace("world","planet")

>>> fruits="apple, banana, cherry, apple"

>>> fruits.replace("apple","orange",1)

>>> sentence="I like apples, Apples are my favorite fruit"

>>> sentence.replace("apples","oranges")