Question about 'None'

[Steven Bethard]

Francis Girard wrote:
>>>>a = "10"
>>>>b = 10
>>>>a > b
> True
> 
>>>>b > a
> False
> 
>>>>id(a)
> 1077467584
> 
>>>>id(b)
> 134536516

Just to thoroughly explain this example, the current CPython 
implementation says that numbers are smaller than everything but None. 
The reason you get such a small id for 'b' is that there is only one 10 
object (for efficiency reasons):

py> 10 is 5 + 5
True
py> 99 is 50 + 49
True
py> 100 is 50 + 50
False

Note that there may be many different instances of integers 100 and 
above (again, in the current CPython implementation).  So to get an 
integer id above a string id, your integer must be at least 100:

py> a = "100"
py> b = 100
py> id(a), id(b)
(18755392, 18925912)
py> a > b
True
py> b > a
False

So, even though b's id is higher than a's, b still compares as smaller 
because the current CPython implementation special-cases the comparison 
to guarantee that numbers are always smaller than all other non-None 
objects.

Again, these are *all* implementation details of the current CPython, 
and depending on these details might run you into troubles if they 
change in a future version of CPython, or if you use a different 
implementation (e.g. Jython or IronPython).

Steve