[Pypgsql-users] Comparing PgNumeric etc. with other data types.

[Adam B. <ad...@po...>]

Hallo,

Recently I found that some PgXXX classes defined in PgSQL module lack
some features I would expect because of the fact that they are
wrappers around PostgreSQL basic data types.  For example, PgNumeric
class is a wrapper around "numeric" type, so it should behave like a
Python number: it should be comparable to other numeric Python types
and it should be usable as a logical value (false when zero and true
when non-zero).  However, PgNumeric values behave differently: they
cannot be compared to other, non-PgNumeric, types/classes and they
always are "true" in logical expressions despite of their real value.
I found the patch on pyPgSQL site which solves the latter problem, but
the first one still exists.

IMHO the most annoying problem is that PgNumeric values cannot be
compared to data values of other type, for example following
expressions:

	PgNumeric('123.45') == None
	PgNumeric('123.45') > 100

raise exceptions instead of returning "false" or "true" (0 or 1).  Of
course, one can write:

	type(PgNumeric('123.45')) == type(None)

but it is not so elegant and differs from what we can write for
standard built-in Python types:

	123.45 == None

Especially comparing values to None is very popular in database
applications as None represents NULL value, am I not right? :)

Since I am going to write some new programs using pyPgSQL library, I
think I could contribute a patch to PgSQL module, which would solve
problems described above.  However I would like to know:

1. if compatibility with Python < 2.1 should be kept (I would like to
use new __lt__, __eq__ etc. method names instead of __cmp__),

2. if PgNumeric, PgInt8 and other wrappers around PostgreSQL numeric
types should be comparable to each other or to standard Python numeric
types (float, long, int) only.

Regards,

-- 
Adam Buraczewski <ad...@po...> * Linux registered user #165585
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