sequence.md

Sequence

What is Sequence?

The Sequence type in Python's typing module is used for type hinting in situations where an ordered collection of items is expected. It's a step towards more precise and readable code, especially when dealing with functions or methods that operate on sequences like lists, tuples, or strings.

To use Sequence, you must first import it:

from typing import Sequence

Basic Usage

Sequence serves as a type hint to indicate that a function parameter, variable, or return type should be a sequence.

Example:

def process_items(items: Sequence[int]) -> None:
    # process the sequence of items here
    ...

Key Characteristics

• Immutability: Sequence is typically used to represent immutable sequences. While you can iterate over and access elements in a Sequence, modifying it is not allowed.

• Generics: As a generic type, Sequence can be parameterized with other types, such as Sequence[str] for a sequence of strings.

• Subtyping: A Sequence is more abstract than specific sequence types like list or tuple. This means a list or tuple can be used where a Sequence is expected, but not vice versa.

• Common Methods: Methods such as __getitem__, __len__, __contains__, index, and count are part of the Sequence interface.

Example 1: ReadOnly Parameter

def sum_sequence(numbers: Sequence[float]) -> float:
    return sum(numbers)

Example 2: ReadOnly Parameter and Mutable Output

def concatenate_strings(strings: Sequence[str]) -> str:
    return ''.join(strings)