Level 6Exercise #133

Preserve an input type

Annotate first() so its return type matches the sequence element type.

What you’ll practice

This Level 6 exercise focuses on TypeVar in the Professional curriculum. Solve the challenge prompt above using clear, idiomatic Python and the relevant language or standard-library tools.

Relevant Python reference: typing — Support for type hints.

Sample Test Cases

Example #1

Input:first([1,2,3])

Output:1 (typed as int)

Reference Solution

Reveal Reference Solution

def first(values: list['T']) -> 'T':
    from typing import TypeVar
    T = TypeVar('T')
    if not values: raise ValueError('empty sequence')
    return values[0]

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Preserve an input type

What you’ll practice

Sample Test Cases

Further Reading

Reference Solution