John Lenton wrote:
On Fri, Feb 11, 2005 at 01:17:55PM -0700, Steven Bethard wrote:
George Sakkis wrote:
"Steven Bethard" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
Is there a good way to determine if an object is a numeric type?
In your example, what does your application consider to be numeric?
Well, here's the basic code:
def f(max=None):
...
while max is None or n <= max:
...
# complicated incrementing of n
So for 'max', technically all I need is <= support. However, the code
also depends on the fact that after incrementing 'n' enough, it will
eventually exceed 'max'. Currently, ints, longs, floats, and Decimals
will all meet this behavior. But I'd rather not specify only those 4
(e.g. with a typecheck), since someone could relatively easily create
their own new numeric type with the same behavior. Do you know a better
way to test for this kind of behavior?
Why don't you express just this need as an assertion?
assert 0 <= max <= max + 1, 'Argument must not be zany'
Well a TypeError might be raised in executing the expression:
py> max = complex(0, 1)
py> assert 0 <= max <= max + 1, 'Argument must not be zany'
Traceback (most recent call last):
File "<interactive input>", line 1, in ?
TypeError: cannot compare complex numbers using <, <=, >, >=
but I do like the max <= max + 1 idea. Maybe I should do something like:
py> def assertnumber(x):
... try:
... 1 < x
... except TypeError:
... raise TypeError('%s is not comparable to int' %
... type(x).__name__)
... try:
... if not x <= x + 1:
... raise TypeError
... except TypeError:
... raise TypeError('%s is not monotonic' %
... type(x).__name__)
...
py> assertnumber(1)
py> assertnumber(1.0)
py> assertnumber(complex(0, 1))
Traceback (most recent call last):
File "<interactive input>", line 1, in ?
File "<interactive input>", line 5, in assertnumber
TypeError: complex is not comparable to int
py> assertnumber('a')
Traceback (most recent call last):
File "<interactive input>", line 1, in ?
File "<interactive input>", line 11, in assertnumber
TypeError: str is not monotonic
py> class C(object):
... def __add__(self, other):
... return 0
... def __lt__(self, other):
... return True
...
py> assertnumber(C())
Traceback (most recent call last):
File "<interactive input>", line 1, in ?
File "<interactive input>", line 11, in assertnumber
TypeError: C is not monotonic
Steve
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