Python, mysql, floating point values question

[mensanator at aol.com]

Christopher Kang wrote:
> I had a question about python and mysql, but I want to first thank
> those who taught me about the factory method, it was exactly what I
> needed.
>
> Anyway, I have a problem where I am pulling floating point values out
> of mysql and into python using the MYSQLdb module.
>
> However, the values seem to be altered a little when I store them in python.
>
> Because the decimal places are off, I am unable to use the values that
> I have in order to write a sql statement (again using the MYSQLdb)
> that pulls column values from just that single value i'm looking for.
>
> Let me explain more clearly:
>
> Let's say I pull column1 values for all records, and they happen to be:
>
> 1.4, 1.5632, 1.32523 in the mysql database.
>
> Now I realize that I am interested in all the column values for just
> the 1.5632 record.  Unfortunately, python seems to be taking the
> floating point values, and doing something with it, such that my
> variable has something like 1.5632000000001 stored in it or such.
>
> I thus, can't pull the value out using a sql statement such as
> "Select * from table_name where column1 = my_variable_value" becuase
> my_variable_value has 1.563200000000001 stored in it, and not 1.5632.
>
> The way that the variable gets adjusted seems to be random.
>
> Is there a solution to this?

The smart-ass answer is to learn how to use floating point properly.

But along those lines, once you get a useful representation of
1.5632 in Python, you may discover that not all the 1.5632's in
the database are identical. They, too, may differ insignificantly.

You may have to apply fixes on both ends. I don't know mysql but
in MS-Acces, I would probably make a calculated field in the db query
such as Format$([TheField],"0.0000"). As a string, the differences
in the many flavors of 1.5632 are discarded.

> 
> 
> 
> Thank you very much!