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

Raymond Hettinger python at rcn.com
Fri Jan 25 20:22:12 CET 2008

If the decision comes to be that int(float) should be blessed as a correct way to truncate a float, I'd agree with Raymond that trunc() is just duplication and should be eliminated.

Yay, we've make progress!

I'd,of course, rather have a spelling that says what it means. :)

I wouldn't fret about this too much. Intrepreting int(f) as meaning truncate has a long history in many programming languages. It is a specious argument int(f) is ambiguous.
No one thinks it means ceil(f).

Go ask a dozen people if they are surprised that int(3.7) returns 3. No one will be surprised (even folks who just use Excel or VB). It is foolhardy to be a purist and rage against the existing art:

SQL: "The INT() function returns its numeric argument with any fractional digits removed and truncates all digits to the right of the decimal point." www.basis.com/onlinedocs/documentation/b3odbc/bbjds_int_function.htm

VB: "Both the Int and Fix functions remove the fractional part of Number and return the resulting integer value." http://msdn2.microsoft.com/en-us/library/xh29swte.aspx

Excel: "The Int function returns the integer portion of a number." http://www.techonthenet.com/excel/formulas/int.php

These docs suggest where the thinking has gone wrong. Writing int(f) doesn't mean "arbritrary select one of round|ceil|floor|trunc as a way of getting to an integer"; instead, it means "return the integer portion (non-fractional component) of a number." The latter definition seems common and is entirely unambiguous.

Raymond

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