7.3 Assignment Operators

=

Plain assignment binds a name to a value — already covered in 4.8 Variables and 6.4 Assignment Operations.

>>> x = 5
>>> x
5

Augmented Assignment

What Is It?

Shorthand combining an arithmetic/bitwise operation with assignment in one step — x += 1 means x = x + 1.

Why Is It Used?

Less repetition, and the intent (“update this variable”) is clearer at a glance.

Quick Interview Answer

“Augmented assignment operators like +=, -=, *= combine an operation with assignment in one step — x += 3 is shorthand for x = x + 3. They exist for both arithmetic (+= -= *= /= //= %= **=) and bitwise operators (&= |= ^= <<= >>=). For an immutable value like an int, x += 1 rebinds x to a new object; for a mutable value like a list, x += [4] mutates the existing object in place via __iadd__ — the same rebind-vs-mutate distinction covered in 6.4 Assignment Operations.”

Common Mistakes

• Assuming x += 1 always mutates in place — for immutable types it rebinds to a new object, which only matters when another variable shares the old reference.
• Chaining augmented assignment across unrelated statements and losing track of the running value — prefer clear, separate steps when the sequence isn’t obvious at a glance.