TypeError: 'bool' object 在使用 all() 时不可迭代

Question

My code is simply to check if list is monotonically increasing or decreasing. I am getting following error,

 TypeError Traceback (most recent call last) <ipython-input-64-63c9df4c7243> in <module> 10 l1 = [75, 65, 35] 11 l2 = [75, 65, 35, 90] ---> 12 is_monotonoc(l) <ipython-input-64-63c9df4c7243> in is_monotonoc(list1) 1 def is_monotonoc(list1): 2 for i in range(len(list1)-1): ----> 3 print(all(list1[i] <= list1[i+1]) or all(list1[i] >= list1[i+1])) 4 5 def isMonotonic(A): TypeError: 'bool' object is not iterable

what is wrong here?

Answer 1

You must have some kind of iterable sequence of items inside the all call. I think you want to get rid of the for-loop and write it into generator expressions inside the all calls.

So where you have:

for i in range(len(list1)-1):
    print(all(list1[i] <= list1[i+1]) or all(list1[i] >= list1[i+1]))

you mean

print(all(list1[i] <= list1[i+1] for i in range(len(list1)-1))
          or all(list1[i] >= list1[i+1] for i in range(len(list1)-1)))

Answer 2

Something like this would do the trick I think.

l1 = [75, 65, 35]
l2 = [75, 65, 35, 90]

def is_monotonoc(list1):
    up=True
    down=True
    for i in range(len(list1)-1):
        if not list1[i] <= list1[i+1]:
            up=False
        if not list1[i] >= list1[i+1]:
            down=False
    print(down or up)

is_monotonoc(l1)
is_monotonoc(l2)

Answer 3

Just capture @Matthis and @khelwood earlier ideas to summarize here: (credit to them, of course): [Note, if the strict in/de-creasing monotonic array is required, then just change x <= y to x < y (or x > y )

def monotonic(lst):
    ''' check if the list is increasing or decreasing'''
    if all(x <= y for x, y in zip(lst, itertools.islice(lst, 1, None))):
        print('List is increasing monotonic list.')
    elif all(x >= y for x, y in zip(lst, itertools.islice(lst, 1, None))):
        print('List is decreasing monotonic list.')
    else:
        print('List is neither increasing nor decreasting monotonic list.')

Outputs:

>>> lst
[75, 65, 55, 40]
>>> monotonic(lst)
List is decreasing monotonic list.
'''