any way to turn off error msg when I catch the errors?

Question

trying to check whether a numerical expression is NaN or not. My expression is log(arcsin(e)). If I apply N() on the expression it goes into infinite loop. I try to catch the runtime error. Everything seems to work in the following code except the error message displayed. I do not want that message in output. Any way to turn the error message off.

sage: def number(expr):
....:         try:
....:             n = N(expr)
....:     except (RuntimeError):
....:             n = N(NaN)
....:     return n
....: 
sage: expr=log(arcsin(e))
sage: a=number(expr)
Exception RuntimeError: 'maximum recursion depth exceeded in __subclasscheck__' in <type 'exceptions.RuntimeError'> ignored
# I do not want the above error message in output
sage: a
NaN
sage: a.is_NaN()
True

Answer 1

This certainly is weird. I think you have an indentation problem in your post, but that doesn't seem to be the problem.

The following is slightly simpler, but also prints the error message for me. (It also prints the error message when I use except RuntimeError)

def number(expr):
    try:    
        n = N(expr)
    except:
        n = 0
    return n

Note, by contrast, that the following works without problem (no error message printed):

def divide(n):
    try:
        r = 1/n
    except ZeroDivisionError:
        r = Infinity
    return r

So it seems this is a bug with the recursion depth RuntimeError . . .

UPDATE: Based on the discussion, I've filed a ticked for this: #10774

Yes, I think it's a bug in Sage: running `N(log(arcsin(e)))`, or just `N(log(NaN))`, seems to send Sage into an infinite loop, hence the error. Can you catch an error produced by an infinite loop? John Palmieri (Feb 11 '11)
Amusingly, complex(log(arcsin(e))) gives 0.82572700817589695+0.81223539737883776j, which works. And you can catch at least some recursion RuntimeErrors; def f(x): f(x) can be caught that way. DSM (Feb 11 '11)
You know, I don't think this _is_ an Exception. I think the reason we can't catch it is because it's been swallowed, and the above is just a print statement. So we'd need to find where it's being printed, and then maybe we could monkeypatch it. DSM (Feb 11 '11)
In any case, I think we're agreed that it's a bug, and a ticket should be filed, right? niles (Feb 11 '11)
Yeah, I think both you and John are right, this is a bug. DSM (Feb 11 '11)

any way to turn off error msg when I catch the errors?

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