Python Math - TypeError NoneType object is not subscriptable

Question

I'm making a small program for math (no particular reason, just kind of wanted to) and I ran into the error "TypeError: 'NoneType' object is not subscriptable.

I have never before seen this error, so I have no idea what it means.

import math

print("The format you should consider:")
print str("value 1a")+str(" + ")+str("value 2")+str(" = ")+str("value 3a ")+str("value 4")+str("\n")

print("Do not include the letters in the input, it automatically adds them")

v1 = input("Value 1: ")
v2 = input("Value 2: ")
v3 = input("Value 3: ")
v4 = input("Value 4: ")

lista = [v1, v3]
lista = list.sort(lista)

a = lista[1] - lista[0]

list = [v2, v4]
list = list.sort(list)

b = list[1] = list[0]

print str(a)+str("a")+str(" = ")+str(b)

The error:

Traceback (most recent call last):
  File "C:/Users/Nathan/Documents/Python/New thing", line 16, in <module>
    a = lista[1] - lista[0]
TypeError: 'NoneType' object is not subscriptable

Answer 1

“TypeError: 'NoneType' object is not subscriptable” is one of the Python errors does not provide a clear answer for new developers.

What this means is that you are trying to use the subscript (or indexing) operator [] on an object that does not support this operation.

The reason it is referring to NoneType is that the response from File.writelines() is None.

Putting all of this together you are attempting to index into None on the line f.writelines(newline)[cnt].

Changing this line to f.write("\nnow") would resolve the issue ("\n" is the shorthard for newline).

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