strange math?

[Steven Bethard]

joe.hrbek at gmail.com wrote:
>>>> f(01)
> 43
>>>> f(02)
> 44
>>>> f(010)
> 50
>>>> 42+010
> 50
> 
> The first f(01) was a mistake.  I accidentally forgot to delete the
> zero, but to my suprise, it yielded the result I expected.  So, I tried
> it again, and viola, the right answer.  So, I decided to really try and
> throw it for a loop, f(010), and it produced 50.  I expected 52
> (42+10).  Why doesn't python ignore the first zero and produce a result
> of 52?  It ignored the first zero for f(01) and f(02).  Hmm.  I know, I
> know, why am I sending it a 01,02, or a 010 to begin with?  Like I
> said, it was an accident, but now i'm curious.  I'm not a computer
> science major so please be kind with any explanations.

Python isn't ignoring the initial 0.  It reads the initial 0 as 
indicating that the following number is expressed in octal.  You can see 
this if you try any number with a digit higher than 7 in it:

 >>> 08
Traceback (  File "<interactive input>", line 1
     08
      ^
SyntaxError: invalid token

So you get 8 added to your number when you write 010 because eight is 
spelled as 10 in octal.

The leading-zero notation is unfortunate, and there has been some recent 
discussion[1][2] on python-dev about trying to change the prefix to 
``0o`` or ``0c`` in Python 3.0 but for the moment at least it looks like 
we're stuck with the confusing leading zero.

[1]http://mail.python.org/pipermail/python-dev/2006-January/060262.html
[2]http://mail.python.org/pipermail/python-dev/2006-February/060277.html

STeVe