What Are Assignment Expressions and How Do They Work with the \"Walrus\" Operator?

Assignment Expressions with the "Walrus" Operator

Since Python 3.8, the "walrus" operator (:=) enables assignment expressions, a significant feature that allows assignments within comprehensions and lambdas.

Rationale for the Introduction of Assignment Expressions

The primary reason behind the introduction of this concept was to facilitate assignments within comprehensions and lambda functions, where traditional assignments are not allowed. Additionally, it enhances interactive debugging, eliminating the need for code restructuring.

Syntax, Semantics, and Grammar

An assignment expression has the form name := expr, where expr is a valid Python expression and name is an identifier. Its value is the same as expr, with the additional side effect of the variable name being assigned that value.

Differences from Regular Assignment Statements:

Assignment expressions differ from regular assignment statements in the following ways:

• Assignment expressions go right-to-left, while regular assignments are evaluated left-to-right.
• Commas have higher precedence in assignment expressions.
• Assignment expressions do not support multiple targets, assignments not to a single name, iterable packing/unpacking, inline type annotations, or augmented assignments.

Examples of Usage

Getting Conditional Values:

<code class="python">while (command := input("> ")) != "quit":
    print("You entered:", command)</code>

Simplifying List Comprehensions:

<code class="python">[[y := x+1, x/y] for x in range(5)]</code>

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