Update of /cvsroot/python/python/nondist/peps In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv10738 Modified Files: pep-0327.txt Log Message: updates from Facundo Batista, with edits Index: pep-0327.txt =================================================================== RCS file: /cvsroot/python/python/nondist/peps/pep-0327.txt,v retrieving revision 1.1 retrieving revision 1.2 diff -C2 -d -r1.1 -r1.2 *** pep-0327.txt 29 Jan 2004 19:59:56 -0000 1.1 --- pep-0327.txt 31 Mar 2004 16:24:00 -0000 1.2 *************** *** 9,13 **** Created: 17-Oct-2003 Python-Version: 2.4 ! Post-History: 30-Nov-2003, 02-Jan-2004 --- 9,13 ---- Created: 17-Oct-2003 Python-Version: 2.4 ! Post-History: 30-Nov-2003, 02-Jan-2004, 29-Jan-2004 *************** *** 401,419 **** affects just operations' results. ! **From int or long**: There's no loss and no need to specify any other ! information:: Decimal(35) Decimal(-124) ! **From string**: Strings with floats in normal and engineering ! notation will be supported. In this transformation there is no loss ! of information, as the string is directly converted to Decimal (there ! is not an intermediate conversion through float):: Decimal("-12") Decimal("23.2e-7") ! **From float**: The initial discussion on this item was what should happen when passing floating point to the constructor: --- 401,430 ---- affects just operations' results. ! ! From int or long ! '''''''''''''''' ! ! There's no loss and no need to specify any other information:: Decimal(35) Decimal(-124) ! ! From string ! ''''''''''' ! ! Strings with floats in normal and engineering notation will be ! supported. In this transformation there is no loss of information, as ! the string is directly converted to Decimal (there is not an ! intermediate conversion through float):: Decimal("-12") Decimal("23.2e-7") ! ! From float ! '''''''''' ! ! The initial discussion on this item was what should happen when passing floating point to the constructor: *************** *** 461,474 **** a substantial risk of tricking naive users. ! So, I think that the best solution is to have a parameter that says in ! which position after the decimal point you apply a round-half-up ! rounding. If you do not specify this parameter, you get an exact ! conversion. In this way:: ! Decimal(1.1, 2) == Decimal('1.1') ! Decimal(1.1, 16) == Decimal('1.1000000000000001') ! Decimal(1.1) == Decimal('110000000000000008881784197001252...e-51') ! **From tuples**: Aahz suggested to construct from tuples: it's easier to implement ``eval()``'s round trip and "someone who has numeric values representing a Decimal does not need to convert them to a --- 472,494 ---- a substantial risk of tricking naive users. ! So, the accepted solution through c.l.p is that you can not call Decimal ! with a float. Instead you must use a method: Decimal.from_float(). The ! syntax:: ! Decimal.from_float(floatNumber, [positions]) ! ! where ``floatNumber`` is the float number origin of the construction and ! ``positions`` is the positions after the decimal point where you apply a ! round-half-up rounding, if any. In this way you can do, for example:: ! Decimal.from_float(1.1, 2): The same that doing Decimal('1.1'). ! Decimal.from_float(1.1, 16): The same that doing Decimal('1.1000000000000001'). ! Decimal.from_float(1.1): The same that doing Decimal('110000000000000008881784197001252...e-51'). ! ! ! From tuples ! ''''''''''' ! ! Aahz suggested to construct from tuples: it's easier to implement ``eval()``'s round trip and "someone who has numeric values representing a Decimal does not need to convert them to a *************** *** 481,492 **** Decimal((1, (3, 2, 2, 5), -2)) # for -32.25 - **From Decimal**: No mystery here, just a copy. ! **Syntax to all the cases**:: ! Decimal(value, [decimal_digits]) ! where ``value`` can be any of the data types just mentioned and ! ``decimal_digits`` is allowed only when value is float. --- 501,522 ---- Decimal((1, (3, 2, 2, 5), -2)) # for -32.25 ! From Decimal ! '''''''''''' ! No mystery here, just a copy. ! ! Syntax for All Cases ! '''''''''''''''''''' ! ! :: ! ! Decimal(value1) ! Decimal.from_float(value2, [decimal_digits]) ! ! where ``value1`` can be int, long, string, tuple or Decimal, ! ``value1`` can be only float, and ``decimal_digits`` is an optional ! int. *************** *** 510,522 **** So, here I define the behaviour again for each data type. - **From int or long**: Aahz suggested the need of an explicit - conversion from int, but also thinks it's OK if the precision in the - current Context is not exceeded; in that case you raise ValueError. - Votes in comp.lang.python agreed with this. ! **From string**: Everybody agrees to raise an exception here. ! **From float**: Aahz is strongly opposed to interact with float, ! suggesting an explicit conversion: The problem is that Decimal is capable of greater precision, --- 540,564 ---- So, here I define the behaviour again for each data type. ! From int or long ! '''''''''''''''' ! Aahz suggested the need of an explicit conversion from int, but also ! thinks it's OK if the precision in the current Context is not ! exceeded; in that case you raise ValueError. Votes in ! comp.lang.python agreed with this. ! ! ! From string ! ''''''''''' ! ! Everybody agrees to raise an exception here. ! ! ! From float ! '''''''''' ! ! Aahz is strongly opposed to interact with float, suggesting an ! explicit conversion: The problem is that Decimal is capable of greater precision, *************** *** 534,538 **** ``Decimal(35) + 1.1`` raises an error). ! **From Decimal**: There isn't any issue here. --- 576,587 ---- ``Decimal(35) + 1.1`` raises an error). ! This resulted to be too tricky. So tricky, that c.l.p agreed to raise ! TypeError in this case: you could not mix Decimal and float. ! ! ! From Decimal ! '''''''''''' ! ! There isn't any issue here.