TypeError: list indices must be integers

[Terry Reedy]

I got this error twice today
while creating lists of lists
of complicated stuff.
The first time I was puzzled,
but the second time I knew
that I had just forgotten a comma.
If you google this, you will too.

Reduced example
 >>> [[1,2,3] # forgot comma
      [4,5,6]]
Traceback (most recent call last):
   File "<pyshell#10>", line 2, in <module>
     [4,5,6]]
TypeError: list indices must be integers, not tuple

Terry Jan Reedy