How Does Python\'s Simple, Extended, and Nested Unpacking Work?

Unpacking, Extended Unpacking, and Nested Extended Unpacking

Unpacking is a convenient way to assign multiple values from an iterable to individual variables in one statement. Python supports three types of unpacking: simple unpacking, extended unpacking, and nested extended unpacking.

Simple Unpacking

• Assigns items in sequence to target variables
• Does not support arbitrary omissions or repetitions
• Example: a, b = 1, 2

Extended Unpacking

• Uses the * operator to collect remaining items into a list
• Can omit or repeat items in the target
• Example: a, *b = 1, 2, 3, 4, 5

Nested Extended Unpacking

• Combines extended unpacking with nested sequences
• Assigns values from the nested sequence to the target variables
• Example: *(a, b) = 1, 2

To correctly deduce the result of these expressions by hand, follow these steps:

1. Convert Iterables to Tuples:

• Assume all iterables are represented as tuples, even if they are not explicitly written with parentheses.

2. Apply Extended Unpacking Rules:

• Variables prefixed with * are assigned a list of remaining items.
• Variables without * are assigned individual items.

3. Resolve Ambiguity in Nested Unpacking:

• If a variable is assigned a nested sequence, it will be unpacked into its individual elements.

Examples:

1. (a, b), c = 1, 2, 3

• Converted: ((a, b), c) = (1, 2, 3)
• Unpacked: a = 1, b = 2, c = 3

2. (a, b), c, = [1, 2], 'this'

• Converted: ((a, b), c) = ((1, 2), 'this')
• Unpacked: a = 1, b = 2, c = 'this'

Notes:

• Multiple * operators within one lvalue are not allowed.
• • targets must be in lists or tuples.
• Empty iterables cannot be assigned to * targets.
• Nested unpacking can lead to ambiguous results.

The above is the detailed content of How Does Python\'s Simple, Extended, and Nested Unpacking Work?. For more information, please follow other related articles on the PHP Chinese website!