On Mon, 19 Aug 2013 22:34:00 +0200, Antoon Pardon wrote: > Op 19-08-13 19:05, Steven D'Aprano schreef: > > >> I wish Python had stronger support for enforcing constantness, to whit, >> some way to say "you can't rebind or delete this name once it is >> bound". You can do it with attributes, by use of property, or in C >> extensions, but you cannot do it with top-level name bindings. It makes >> me terribly sad that you can do this: >> >> import math >> math.pi = 3.0 >> >> >> although I can't decide whether I am less sad or more sad to see that >> the behaviour of math.sin and friends doesn't depend on math.pi. > > Why should you expect math.sin and friends be dependant on math.pi? > AfAIR the numerical algorithms for calulating sin and friends don't > depend on (the value of) pi. So there is no reason to suspect that > altering math.pi would have any effect on the results of these > functions.
Of course they depend on pi. Or rather, they depend on the geometric properties of circles, which are related to pi. If the ratio of the circumference of a circle to its diameter was exactly 3, instead of 3.1415..., then sine and cosine functions would be periodic with period 6 rather than τ = 2π. If you consider the implementation of sin and cos functions, they usually reduce the argument modulo π to something in the first quadrant, and then use symmetry to adjust the value. So changing the value of pi could, in principle, change the implementation of sin, cos and tan. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
