The curious behavior of integer objects

[Gabriel Genellina]

At Monday 15/1/2007 19:28, Jim B. Wilson wrote:

>Am I nuts? Or only profoundly confused? I expected the this little script
>to print "0":
>
>class foo(int):
>   def __init__(self, value):
>     self = value & 0xF
>
>print foo(0x10)
>
>Instead, it prints "16" (at least on python 2.4.4 (Linux) and 2.5 (Wine).

Integers are immutable. Insert a print statement and you'll see your 
__init__ is never called. Anyway, what would you expect from "self = 
something"?
Use __new__ instead:

py> class foo(int):
...   def __new__(cls, value):
...     return int(value & 0xF)
...
py> foo(1)
1
py> foo(0x10)
0

See "Special method names" inside the Python Reference Manual.


-- 
Gabriel Genellina
Softlab SRL 


	

	
		
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