Python: Finding neighbouring duplicates in a list-CodePudding

First things first...I am Python newbie...so I apologize, if this is maybe the most basic question you have ever seen here. Fundamentally, I want to solve a question from a Kaggle Python (beginner) course to solve the following challenge:

def menu_is_boring(meals):

    """Given a list of meals served over some period of time, return True if the
    same meal has ever been served two days in a row, and False otherwise.
    """

I created the following nested for loop. The idea was that I can compare this way the list to itself and the moment I find a duplicate it returns true:

for i in range(len(meals)):
        for j in range(i 1, len(meals)):
            if j == i:
                return True
    return False

The input is: meals=['Spam', 'Eggs', 'Spam', 'Spam', 'Bacon', 'Spam']

So I would anticipate a "True" (2X Spam in a row), but my function returns a False. It looks sooo easy..but apparently I am missing something. Maybe there is something fundamental about nested loops that I am missing here. I googled other problems where nested loops are used for duplicated...but cant see an obvious difference to what I did.

CodePudding user response：

An easier solution is to just use one loop and use i 1 as your second index, but note that you have to reduce the length of your loop, because otherwise you get out of bound at the last loop cycle.

for i in range(len(meals) - 1):
    if meals[i] == meals[i   1]:
        return True
# iff no same meals at two days the loop doesnt return True
# and after loop is finished execute next code, which is return False
return False

CodePudding user response：

Another way to handle this is to use the zip() function to tie the original list to an 1-offset of the original list and compare the values as if a == b.

For example:

def test(items: list):
    return any(a==b for a, b in zip(items, items[1:]))

This builds a generator expression of boolean values. The any() function will 'short circuit' and return immediately once a True value is found; thus making this function quite efficient.

Output:

>>> meals = ['Spam', 'Eggs', 'Spam', 'Spam', 'Bacon', 'Spam']
>>> test(meals)

True