def number(lines):
    """
    Your team is writing a fancy new text editor and you've been tasked with implementing the line numbering.
    Write a function which takes a list of strings and returns each line prepended by the correct number.
    The numbering starts at 1. The format is n: string. Notice the colon and space in between.
    """

    return [f'{index}: {value}' for index, value in enumerate(lines, 1)]