how to check if a string contains letters in python code example

Example 1: check if string contains python

>>> str = "Messi is the best soccer player"
>>> "soccer" in str
True
>>> "football" in str
False

Example 2: python check if string contains substring

string = "My favourite programming language is Python"
substring = "Python"

if substring in string:
    print("Python is my favorite language")
elif substring not in string:
    print("Python is not my favourite language")