How to Efficiently Check if All Elements in a Python List are Equal?

Checking Equality of Elements in a List

To determine whether all elements in a list are equal, we need to iterate through the list and evaluate their equality using the standard equality operator. A Pythonic approach to this problem is to use boolean operations and iterators.

Solution 1: Using Iterators and Groupby

One efficient solution is to leverage itertools.groupby, which groups adjacent elements with equal values. The following function utilizes groupby to verify if all elements are equal:

from itertools import groupby

def all_equal_groupby(iterable):
    g = groupby(iterable)
    return next(g, True) and not next(g, False)

Solution 2: Alternative Iterators

Alternatively, we can use iterators to iterate through the list and perform element-by-element comparisons:

def all_equal_iter(iterator):
    iterator = iter(iterator)
    try:
        first = next(iterator)
    except StopIteration:
        return True
    return all(first == x for x in iterator)

Performance Considerations

The choice of solution depends on the specific requirements of the problem. For large lists or where early termination is desired (if an inequality is found), the groupby-based solution is more efficient. However, if memory usage is a concern, the iterator-based solution is preferable.

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