In Python, is and == are both comparison operators that can be used to check if two values are equal.
Key Differences Between is and ==
| Feature | is |
== |
|---|---|---|
| Purpose | Checks identity (same memory location). | Checks equality (same value). |
| Returns | True if objects are the same instance. |
True if objects have the same value. |
| Use Case | Verify if two references point to the same object. | Compare data for equality. |
| Example with Lists | a is b returns False for two separate but equal lists. |
a == b returns True for lists with the same contents. |
Example 1: Immutable Objects
# Immutable integers
a = 1000
b = 1000
print(a == b) # True (values are the same)
print(a is b) # False (different memory locations for large integers)
# Small integers (Python caches -5 to 256)
x = 100
y = 100
print(x == y) # True
print(x is y) # True (both point to the same cached object)
# Strings
s1 = "hello"
s2 = "hello"
print(s1 == s2) # True
print(s1 is s2) # True (string interning reuses memory)Example 2: Mutable Objects
# Mutable lists
a = [1, 2, 3]
b = [1, 2, 3]
print(a == b) # True (values are the same)
print(a is b) # False (different objects in memory)
# Same object reference
c = a
print(a is c) # True (both refer to the same object)Example 3: None Comparisons
The is operator is often used to compare with None because None is a singleton in Python.
a = None
print(a is None) # True
print(a == None) # True, but using `is` is preferred stylistically.PEP 8 recommends using is for None checks, because it’s explicit and slightly faster.
When to Use is vs ==
- Use
is:- To check if two variables refer to the same object.
- Comparing with
None:if obj is None: - Verifying identity of singletons or cached objects.
- Use
==:- To check if the values of two variables are equal.
- Suitable for most comparisons involving data structures (lists, strings, dictionaries, etc.).
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