Membership Operators

Membership operators test whether something appears inside a collection: in and not in.

in

python
fruits = ["apple", "banana"]
print("banana" in fruits)

### True
print("grape" in fruits)

### False

Works on strings too

python
txt = "The best things in life are free!"
print("free" in txt)

### True

not in

python
print("grape" not in fruits)

### True
print("banana" not in fruits)

### False

Works on any collection

• strings, lists, tuples, sets, dictionaries (checks keys), ranges.

python
print(3 in (1, 2, 3))

### True
print(2 in range(5))

### True
print("a" in {"a": 1})

### True (checks keys)

In an if

python
if "apple" in fruits:
    print("We have apples!")

TL;DR

• in returns True if a value is inside a collection.
• not in returns the opposite.
• Works on strings, lists, tuples, sets, dicts (keys), ranges.