Reimplementation of min() in Python

Question

I'm reimplementing the min() function as an exercise (EDIT: not all the functionality of the python std library function, just the minimum of a list of numbers). Here is my code:

def my_min(num_list):
    minimum = num_list[0]
    for num in num_list[1:]:
        if num < minimum:
            minimum = num            
    return minimum

My question is: How bad is num_list[1:] in the for loop? And are there any other optimizations I could make to the code?

My intention by truncating the list is to avoid comparing the list's first element to itself. While insignificant in terms of wasted time and resources, I just find it lacking elegance.

Answer 1

iterators

You can use an iterator

def my_min(num_list):
    # empty lists
    if not num_list:
        raise ValueError('Empty list')

    list_iter = iter(num_list)
    minimum = next(list_iter)
    for num in list_iter:
        if num < minimum:
            minimum = num            
    return minimum

In response to Mathias' comment, here is a version that works with an iterable:

def my_min(seq):
    seq = iter(seq)

    try:
        minimum = next(seq)

        for num in seq:
            if num < minimum:
                minimum = num            

        return minimum

    except StopIteration as e:
        pass

    raise ValueError('Empty list')

Improved based on @Wombatz comment:

def my_min(seq):
    seq = iter(seq)

    try:
        minimum = next(seq)

    except StopIteration as e:
        raise ValueError('Empty list') from None

    else:
        for num in seq:
            if num < minimum:
                minimum = num            

        return minimum

Answer 2

Review

I should check for the list having no elements anyway, so I could check for its having only 1 element and return that element

• You have implemented a simple function, so it shouldn't have been that hard to provide a couple of unit tests. You would have immediately found bugs on the most obvious edge cases as (1) empty list and self-created edge case (2) single item.

While insignificant in terms of wasted time and resources, I just find it lacking elegance.

• What you gain in elegance is lost by the edge case guards you'd have to build in to fix the bugs.