How do you check if a string has a specific letter python code example

Example 1: if substring not in string python

fullstring = "StackAbuse"
substring = "tack"

if fullstring.find(substring) != -1:
    print "Found!"
else:
    print "Not found!"

Example 2: if substring not in string python

>>> string = "Hello World"
>>> # Check Sub-String in String
>>> "World" in string
True
>>> # Check Sub-String not in String
>>> "World" not in string
False

Example 3: python check if string contains one of characters list

if any(ext in url_string for ext in extensionsToCheck):
    print(url_string)