Python Membership Operators

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Membership Operators are used to test whether a value or variable is found in a sequence (string, list, tuple, set, or dictionary). The operators are either 1. In or 2. Not in.

Example:

I’m going to create a “secret” word – say APPLE. Let’s make a game where the user has to guess a letter. After the user inputs a letter, we want to check to see if the letter selected is found in the word. We need a Boolean TRUE if it is and FALSE if it’s not:

word = "APPLE"
letter = input("Guess a letter in the secret word: ")

if letter in word:
   print(f"There is a {letter}")
else:
   print(f"{letter} was not found")

Conversely, we can use the not in operator:

word = "APPLE"
letter = input("Guess a letter in the secret word: ")

if letter not in word:
   print(f"{letter} was not found")
else:
   print(f"There is a {letter}")

Using a set:

students = {"Spongebob", "Patrick", "Sandy"}

student = input("Enter the name of a student: ")

if student in students:
   print(f"{student} is in this class")
else:
   print(f"{student} is NOT in this class")

Using a dictionary of student grades:

grades = {
   "Sandy": 'A',
   "Squidward": 'B',
   "Spongebob": 'C',
   "Patrick": 'D'
}

student = input("Enter the name of a student: ")

if student in grades:
   print(f"{student}'s grade is {grades[student]}.")
else:
   print(f"{student} is not in the dictionary")

Outputs:

Enter the name of a student: Sandy
Sandy's grade is A.

Using a string:

email = "bobdown@gmail.com"

if "@" in email and "." in email:
    print("Valid email")
else:
    print("Invalid email")

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