-3

I want to check if a certain range in a list is the same. For example: In a list I have [X,Y,X,X,X,Y,Y], and I want to see if the third, fourth, and fifth are the same.

I have tried the following:

list = ['X', 'Y', 'X', 'X', 'X', 'Y']
for i in list, range(2,4):
    if not i == 'X':
        print("Test")

It does work, prints Test twice.

Test
Test

I just don't want to write a bunch of this:

if ... and .... and ..... and ... or .... and ...

martineau
  • 112,593
  • 23
  • 157
  • 280
Beni Rae
  • 3
  • 1
  • 1
    That's not how you slice lists. Read [Python's list slice notation](https://stackoverflow.com/questions/509211/understanding-pythons-slice-notation) to learn how. What you are actually doing is forming a tuple `(list, range(2, 4))` and iterating over that. Neither of those values is equal to `X`, so it prints twice. As an aside "not equals" is more naturally expressed as `i != 'X'` – Patrick Haugh Jul 09 '18 at 02:19

2 Answers2

2

You are looping such that you test not list == 'X' then not range(2, 4) == 'X'; obviously, neither is equal, so you print both times. Your logic can be dramatically simplified though. If the goal is to see if indices 2, 3 and 4 are all equal, just convert that slice of the list to a set and check if the length is 1:

mylist = ['X', 'Y', 'X', 'X', 'X', 'Y']  # Changed list name; naming the list "list" leads to tears
if len(set(mylist[2:5])) == 1:
    print("2, 3 and 4 equal")
else:
    print("At least one not equal to the others")

You may also wish to check that mylist is long enough (slicing will not raise an error if the slice doesn't get the three elements expected), as written this only tests that the list is at least 3 elements long and any elements from index 2 to 4 are equal if they exist.

ShadowRanger
  • 124,179
  • 11
  • 158
  • 228
0

I'm sure there is more elegant way to do that, but you can try that:

def check_same(mylist, start_index, end_index):
    value = mylist[start_index]   
    for element in mylist[start_index + 1 : end_index]:
    if not element == value:
        return False
    return True
Reblochon Masque
  • 33,202
  • 9
  • 48
  • 71
Egor Sergeevich
  • 1