Hi all,
I'm having a "will this cause too much surprise" question here.
I need to explain the situation, so I'm sorry for any tl;dr effects.
as those who're watching https://github.com/sympy/sympy/pull/911 already
know, I have upgraded raises() by backporting some code from pytest.
Raises will then be able accept code in three forms:
As a string like before:
raises(DivisionByZero, "1/0")
As a lambda:
raises(DivisionByZero, lambda: 1/0)
The code inside the lambda does not execute before raises() is called,
but inside raises(), after all the mechanics has been set up to catch
any exceptions and report them if they aren't the expected one.
As a with statement:
with raises(DivisionByZero):
1/0
This works just like the lambda but can contain statements (assignments,
loops etc.)
Now the question is what people would do it they have two such tests to
run. For a silly example, assume testing whether 1/0 and -1/0 both throw
an exception. Would you write
with raises(DivisionByZero):
1/0
with raises(DivisionByZero):
-1/0
or
with raises(DivisionByZero):
1/0
-1/0
The potential issue here is that if people instinctively use the second
form, they won't get the -1/0 test: the 1/0 will raise the exception and
shortcut the entire with block.
Now the question is whether that's a problem in practice or not.
Points to consider:
- That an exception shortcuts the entire with block is part of the
intended purpose of with blocks, so we might say we're expecting
everybody using them to know their semantics.
- This construction with the exact same semantics is also available in
pytest. So the pytest people either consider the issue to be a
nonproblem, or they have accepted it as a necessary evil. (Is anybody
able to dig up any discussion the pytest people might have had on the
issue?)
- Those who get hit by this won't notice. There won't be an error
message, just a slightly worse test coverage.
- It's a rare problem. I have applied the new lambda: and with: stuff to
99% of all tests in SymPy, and less than a dozen or so tests actually
had statements in them. With a lambda, nobody is going to make this error.
Should we worry, or not?
Any feedback welcome.
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