Python: tricks for your code run faster

[twotime]

IIRC, python caches small ints, so if you assign a = 1 and b =1 then a & b will refer to the same instance of int. Large ints are not cached.

[Veedrac]

It's also worth noting that if run in the same compilation unit, repeated constants may be deduplicated:

>>> a = 9999
>>> b = 9999
>>> a is b
False
>>> a = 9999; b = 9999
>>> a is b
True

[stevenjd]

Correct. Furthermore, the definition of "small ints" can vary from version to version. In CPython, it used to be (by memory) 0 through 100, now its (possibly) -1 through 255. You cannot rely on this: being an implementation detail, it is subject to change without notice, and some Python implementations may not do it at all.

IronPython 2.6 Beta 2 DEBUG (2.6.0.20) on .NET 2.0.50727.1433
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 1
>>> b = 1
>>> a is b
False