Python semi-noob, can someone explain why this phonomena occurs in 'Lists'

Question

I'm working on a small app that pulls data out of a list stored in a list, passes it through a class init, and then displays/allows user to work. Everything was going fine until i tried to format the original 'list' in the IDLE so it was easier to read (for me). so I'd change 9 to 09, 8 to 08. etc It was a simple formating/spacing change and it broke the entire god damn program, citing 'invalid token'. WTF is this, I thought. So then I opened the interpreter and started typing:

>x = [5,5]  #Control

>x

[5, 5]

>>> y=[05,05]    #control2

>>> y

[5, 5]

>>> z = [05, "ge"]  #test. 'Integer', before string, apparantly works.


>>> z

[5, 'ge']

> a = ["ge", 09]  #test2. String, before 'integer', cocks things up.

SyntaxError: invalid token

>>> b= ["ge", 9]    #test3, this works fine.


>>> b


['ge', 9]

I guess my question is... why does this occur? Why is python interpret these integers as 'tokens' when they follow strings, but as integers when they follow integers?

Answer 1

It's nothing to do with lists or strings. When you prefix a number with 0, it's interpreted as octal. And 9 is not a valid octal digit!

Python 2.7.6 
Type "help", "copyright", "credits" or "license" for more information.
>>> 09
  File "<stdin>", line 1
    09
     ^
SyntaxError: invalid token
>>> 011
9

Note that in Python3, this gives you the error for any 0-prefixed number, presumably to reduce confusion of the type you are experiencing. To specify octal in Python3, you must use 0o as a prefix.

Python 3.3.3 
Type "help", "copyright", "credits" or "license" for more information.
>>> 09
  File "<stdin>", line 1
    09
     ^
SyntaxError: invalid token
>>> 011
  File "<stdin>", line 1
    011
      ^
SyntaxError: invalid token
>>> 0o11
9
>>> 0o9
  File "<stdin>", line 1
    0o9
     ^
SyntaxError: invalid token
>>>