Python: TypeError: 'int' object is not subscriptable

Question

I get a TypeError and I don't understand why. The error is at c = t[i][0] (according to the debugger). I have 3 char groups(lists): g1, g2 and g3 and I'm trying to change the char's index by substracting the key's k1, k2 or k3 from the index. What I'm using now for testing:

text = 'abcd'

l_text = [('a', 0), ('b', 1), ('c', 2), ('d', 3)]

k1, k2, k3 = 2, 3, 1

And this is the code:

def rotate_left(text, l_text, k1, k2, k3):
    i = 0
    newstr = [None]*len(text)
    for t in l_text: # t = tuple
        c = t[i][0] 
        if c in g1: # c = char
            l = int(l_text[i][1]) # l = index of the char in the list
            if l - k1 < 0:
                newstr[l%len(text)-k1] = l_text[i][0]
            else:
                newstr[l-k1] = l_text[i][0]
        elif c in g2:
            l = l_text[i][1] # l = index of the char in the list
            if l - k1 < 0:
                newstr[l%len(text)-k2] = l_text[i][0]
            else:
                newstr[l-k2] = l_text[i][0]
        else:
            l = l_text[i][1] # l = index of the char in the list
            if l - k1 < 0:
                newstr[l%len(text)-k3] = l_text[i][0]
            else:
                newstr[l-k3] = l_text[i][0]
        i += 1
    return newstr

Can someone explain me why do I get this error and how do I fix it? It's not like I'm using an int type there. The debugger shows it's a str type and it breaks after the 2nd iteration.

PS google didn't help PPS I know there is too much repetition in the code. I did it to see in the debugger what's happening.

UPDATE:

Traceback (most recent call last):
  File "/hometriplerotatie.py", line 56, in <module>
    print(codeer('abcd', 2, 3, 1))
  File "/home/triplerotatie.py", line 47, in codeer
    text = rotate_left(text, l_text, k1, k2, k3)
  File "/home/triplerotatie.py", line 9, in rotate_left
    c = t[i][0] 
TypeError: 'int' object is not subscriptable

Answer 1

You are indexing into each individual tuple:

c = t[i][0] 

i starts out as 0, but you increment it each loop iteration:

i += 1

The for loop is binding t to each individual tuple from l_text, so first t is bound to ('a', 0), then to ('b', 1), etc.

So first you are looking at ('a', 0)[0][0] which is 'a'[0] which is 'a'. The next iteration you look at ('b', 1)[1][0] which is 1[0] which raises your exception, because integers are not sequences.

You need to remove the i; you do not need to keep a running index here as the for t in l_text: is already giving you each individual tuple.

Answer 2

The error is here:

l_text = [('a', 0), ('b', 1), ('c', 2), ('d', 3)]

...

for t in l_text: # t = tuple
    # t is a tuple of 2 items: ('a', 0)
    c = t[i][0] # Breaks when i == 1

I think you want:

c = t[0]

It doesn't break the first time round the loop because when i == 0, t[i] is 'a' and then t[i][0] is also 'a'.

Answer 3

You are doing the index part wrong. Your tuple is 1 dimensional, so you cant use a 2-D array subscript notation. Assuming that

t = ('a',0)

you should use t[0] or t[1] to access a and 0 respectively.

Hope it helps.. :)

Answer 4

The problem is that t is a tuple, you access the elements in a tuple that like a list. Currently you acces the elements like a 2D list which would, given your lists result in trying to indexing a char.

for t in l_text: # t = tuple
    c = t[i][0]

should be changed to

for t in l_text: # t = tuple
    c = t[0]