[Python-Dev] trunc() (original) (raw)

Guido van Rossum guido at python.org
Thu Jan 24 21:08:09 CET 2008

On Jan 24, 2008 11:36 AM, "Martin v. Löwis" <martin at v.loewis.de> wrote:

> trunc() has well-defined semantics -- it takes a Real instance and > converts it to an Integer instance using round-towards-zero semantics.

No. trunc calls trunc, which does whatever it pleases to do. >>> class A: ... def trunc(self): ... return 0 ... >>> a=A() >>> trunc(a) 0

However, PEP 3141 specifies what it should do for Numbers.

> int() has undefined semantics -- it takes any object and converts it > to an int (a concrete type!) using whatever rules it likes -- the > definition of int is up to whatever the source type likes to do. > For float this has been defined the same as trunc() above, but for > other types, who knows! int() of a string does something completely > different.

But why is that a reason to keep trunc()? If you only ever want to convert floats to ints, you can use either one, with no difference. int() does not have undefined semantics, for floats, it converts it to an integer using round-towards-zero semantics.

Yes (although it wasn't always specified this way). But I don't like that, because of the ambiguity of int(x).

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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