Alex, I think you're missing a point here: what you are looking
for is an interface, not a base class - simply because the
assumptions you make when finding a "KnownNumberTypes" instance
are only related to an interface you expect them to provide.
A common case class won't really help all that much with this,
since the implementations of the different types will vary a
lot (unlike, for example, strings and Unicode, which implement
a very common interface) and not necessarily provide a common
interface.
If you look at the Python C API, you'll find that "a number"
is actually never tested. The tests always ask for either
integers or floats.
The addition of a basenumber base class won't make these any
simpler.
Here's a snippet which probably does what you're looking for
using Python's natural way of hooking up to an implicit
interface:
import UserString
STRING_TYPES = (basestring, UserString.UserString)
def floatnumber(obj):
if isinstance(obj, STRING_TYPES):
raise TypeError('strings are not numbers')
# Convert to a float
try:
return float(obj)
except (AttributeError, TypeError, ValueError):
raise TypeError('%r is not a float' % obj)
def intnumber(obj):
if isinstance(obj, STRING_TYPES):
raise TypeError('strings are not numbers')
# Convert to an integer
try:
value = int(obj)
except (AttributeError, TypeError, ValueError):
raise TypeError('%r is not an integer' % obj)
# Double check so that we don't lose precision
try:
floatvalue = floatnumber(obj)
except TypeError:
return value
if floatvalue != value:
raise TypeError('%r is not an integer' % obj)
--
Marc-Andre Lemburg
eGenix.com
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