[Python-ideas] Inline 'raises' expression

[Mathias Panzenböck]

Fredrik Johansson schrieb:
> Hi,
>
> It happens that I'm just interested in whether an expression raises an
> exception, not the return value. This might look something like
>
>     try:
>         check_status()
>     except IOError:
>         cleanup()
>
> which could be written more simply as
>
>     if check_status() raises IOError:
>         cleanup()
>
> Also, instead of the inconvenient
>
>     self.assertRaises(ZeroDivisionError, lambda: 1/0)
>
> one could just write
>
>     assert 1/0 raises ZeroDivisionError
>
> Something like this would especially be useful for those of us who
> aren't fans of the unittest framework. Alternatively, just the
> assert--raises form could be permitted.
>
> Thoughts?
>
> Fredrik

I think an extra syntax for such an easy task is unnecessary.
The following function emulates this functionality sufficiently:

def raises(f,e):
	try:
		f()
	except e:
		return True
	except:
		return False
	else:
		return False

def f(x):
	if x != 2:
		raise ValueError()

>>> raises(lambda:f(1),ValueError)
True
>>> raises(lambda:f(2),ValueError)
False
>>> raises(lambda:f(1),Exception)
True
>>> raises(lambda:f(2),Exception)
False
>>> raises(lambda:f(1),TypeError)
False
>>> raises(lambda:f(2),TypeError)
False