Re: problem with money datatype based calculations in python
On Sun, 2009-05-03 at 03:20 +, D'Arcy J.M. Cain wrote: Sorry, I should have mentioned my bias. :-) No problems at all. It is a very good library. I get an impression that it is realy a mature module and a very powerful set of API. I would like to know if it has been tested with postgresql 8.3 and are The current version of PyGreSQL has been tested with Python 2.5 and PostGreSQL 8.3. Older version should work as well, but you will need at least Python 2.3 and PostgreSQL 7.4. Ah, I am using python 2.6 and postgresql 8.3 I am really impressed with the library. I want some manual or tutorial for the same and if possible can you write me off the list with a small tutorial for things like connecting to the database, sending queries, and working with the resultset at the client site. I will be really happy if this library also supports calling a stored procedurs directly. Psycopg2 does not have such a feature and I had to create one small module which does that work. What it does is that you just give the name of the procuedure procedure as the first parameter and a list of arguements as the second parameter. That's all, you will get the result because the query for the call is created inside the module and the programmer need not worry about what the sored procedure looks like. Never the less I am expecting that pygresql has some infrastructure for making calls to the stored procedures. Please send me some tutorial off the list. happy hacking. Krishnakant. -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
Krishnakant krm...@gmail.com wrote: ['money datatype' for database stored values] What ist the real problem? Do you have problems converting results of float calculations to the 'money datatype' before storing them in the database, or do you want to avoid the precision issues which come with the conversion od non-integer values between binary and decimal? In the latter case use the Decimal data type from module decimal (comes with the python distribution -- it is mentioned in the tutorial). Regards, Günther -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
Do calculations in postgresql and then call that calculated value from the python.So no need to calculate in python at all Njoy the share of Freedom, Anusha Kadambala On Sat, May 2, 2009 at 1:15 PM, Krishnakant krm...@gmail.com wrote: hello all, I am using postgresql as a database server for my db application. The database is related to accounts and point of sales and many calculations involve money datatype. The application logic is totally done in python. Now the problem is that there is a situation where we calculate tax on % of the total amount on the invoice. The percentage is in terms of float but the eventual amount has to be in a money datatype. The product cost comes in money datatype from postgresql and the tax % comes in float. So I would like to know if python supports some thing similar to money datatype so that I can cast my total amount (in money ) divided by tax% (in float ) so money divided by float should be the result and that result should be in money datatype. For example a product x has the cost Rs. 100 which is stored in the tabel as money type. and in the tax table for that product the VAT is 5% and this 5% is stored in float datatype. So after using both these values the resulting total 105Rs. should be in money type and not float. I awaite some reply, Thanks in advice. happy hacking. Krishnakant. -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
Krishnakant wrote: hello all, I am using postgresql as a database server for my db application. The database is related to accounts and point of sales and many calculations involve money datatype. The application logic is totally done in python. Now the problem is that there is a situation where we calculate tax on % of the total amount on the invoice. The percentage is in terms of float but the eventual amount has to be in a money datatype. The product cost comes in money datatype from postgresql and the tax % comes in float. So I would like to know if python supports some thing similar to money datatype so that I can cast my total amount (in money ) divided by tax% (in float ) so money divided by float should be the result and that result should be in money datatype. For example a product x has the cost Rs. 100 which is stored in the tabel as money type. and in the tax table for that product the VAT is 5% and this 5% is stored in float datatype. So after using both these values the resulting total 105Rs. should be in money type and not float. I awaite some reply, Thanks in advice. happy hacking. Krishnakant. Tax rate isn't divided, it's multiplied. But probably that's just a typo in your message. Short answer is use your money class to convert the float into money. And then test, to see that's really what you wanted. Be sure and check the edge cases, because float is a binary system, and you can get both quantization and rounding problems converting between them. Is the money you're dealing with decimal-based? So maybe money values are integers plus two more digits of fractional precision? It's going to be tough for somebody with no access to that money type to guess what your problem is. What operations does it currently support? If it supports multiply, then just change the tax rate to be a money type. Unless of course you might have a tax rate of 5.221% Does your money class support accurate conversion to class decimal? In that case, convert to decimal, multiply, then convert back. Or if money is really a fixed-point class, with assumed two digits, multiply the cost by 100 and convert to int. Multiply by the tax, and convert back. You also need to specify the government rules for the multiply. Is rounding permitted, or must all fractions of a penny (assumption there) be rounded up? Or switch everything to class decimal in the standard python library, You still have most of the questions to answer, but at least you'd be asking on the right forum. -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
On Sat, 02 May 2009 15:43:23 +0200 Günther Dietrich guenther.dietr...@spamfence.net wrote: Krishnakant krm...@gmail.com wrote: ['money datatype' for database stored values] What ist the real problem? Do you have problems converting results of float calculations to the 'money datatype' before storing them in the database, or do you want to avoid the precision issues which come with the conversion od non-integer values between binary and decimal? In the latter case use the Decimal data type from module decimal (comes with the python distribution -- it is mentioned in the tutorial). And if you use PyGreSQL (http://www.PyGreSQL.org/) to connect to the database then the money type is already converted to Decimal. -- D'Arcy J.M. Cain da...@druid.net | Democracy is three wolves http://www.druid.net/darcy/| and a sheep voting on +1 416 425 1212 (DoD#0082)(eNTP) | what's for dinner. -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
On Sat, 02 May 2009 13:15:22 +0530, Krishnakant krm...@gmail.com wrote: hello all, I am using postgresql as a database server for my db application. The database is related to accounts and point of sales and many calculations involve money datatype. [snip] As far as I can tell, Python has no type money. Is money a class defined by some postgresql module you're using? A very small amount of specific information (e.g., a five-line sample program that demonstrates the problem) would greatly improve your chances of getting useful help. -- To email me, substitute nowhere-spamcop, invalid-net. -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
On Sat, 2009-05-02 at 11:57 -0400, D'Arcy J.M. Cain wrote: And if you use PyGreSQL (http://www.PyGreSQL.org/) to connect to the database then the money type is already converted to Decimal. d'arcy, I visited the home page for pygresql and discovered that you wrote the library. I am happy that you also included a non-dbapi (postgresql classic interface ) along with the standard DBAPI module. I would like to know if it has been tested with postgresql 8.3 and are there any known bottlenecks while using this driver module on large scale database opperations? Is this actively maintained? Perhaps this might be off topic but may I ask, how is pypgsql, Has any one used pgsql for any postgresql based software? and between pygresql and pypgsql which one is more maintained? the system I am developing is a mission critical financial application and I must be pritty sure about any module I am using. happy hacking. Krishnakant. -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
On May 3, 12:09 am, Dave Angel da...@ieee.org wrote: Krishnakant wrote: hello all, I am using postgresql as a database server for my db application. The database is related to accounts and point of sales and many calculations involve money datatype. The application logic is totally done in python. Now the problem is that there is a situation where we calculate tax on % of the total amount on the invoice. The percentage is in terms of float but the eventual amount has to be in a money datatype. The product cost comes in money datatype from postgresql and the tax % comes in float. So I would like to know if python supports some thing similar to money datatype so that I can cast my total amount (in money ) divided by tax% (in float ) so money divided by float should be the result and that result should be in money datatype. For example a product x has the cost Rs. 100 which is stored in the tabel as money type. and in the tax table for that product the VAT is 5% and this 5% is stored in float datatype. So after using both these values the resulting total 105Rs. should be in money type and not float. I awaite some reply, Thanks in advice. happy hacking. Krishnakant. Tax rate isn't divided, it's multiplied. But probably that's just a typo in your message. Short answer is use your money class to convert the float into money. And then test, to see that's really what you wanted. Be sure and check the edge cases, because float is a binary system, and you can get both quantization and rounding problems converting between them. Is the money you're dealing with decimal-based? So maybe money values are integers plus two more digits of fractional precision? It's going to be tough for somebody with no access to that money type to guess what your problem is. What operations does it currently support? If it supports multiply, then just change the tax rate to be a money type. Aarrgghh!! If the money type supports multiplying money by money, the author should be put in the stocks and pelted with rotten vegetables. (IMHO) -- http://mail.python.org/mailman/listinfo/python-list
Re: problem with money datatype based calculations in python
On Sun, 03 May 2009 00:07:17 +0530 Krishnakant krm...@gmail.com wrote: On Sat, 2009-05-02 at 11:57 -0400, D'Arcy J.M. Cain wrote: And if you use PyGreSQL (http://www.PyGreSQL.org/) to connect to the database then the money type is already converted to Decimal. d'arcy, I visited the home page for pygresql and discovered that you wrote the library. Sorry, I should have mentioned my bias. :-) I am happy that you also included a non-dbapi (postgresql classic interface ) along with the standard DBAPI module. That interface existed before there was a DB-API spec. We added the DB-API interface later and decided to support both. I would like to know if it has been tested with postgresql 8.3 and are The current version of PyGreSQL has been tested with Python 2.5 and PostGreSQL 8.3. Older version should work as well, but you will need at least Python 2.3 and PostgreSQL 7.4. there any known bottlenecks while using this driver module on large scale database opperations? None that I know of. It is used on some pretty big databases that I know of. Is this actively maintained? Yes. I'll leave the rest of the questions for someone less biased. :-) -- D'Arcy J.M. Cain da...@druid.net | Democracy is three wolves http://www.druid.net/darcy/| and a sheep voting on +1 416 425 1212 (DoD#0082)(eNTP) | what's for dinner. -- http://mail.python.org/mailman/listinfo/python-list
