On Friday, April 27, 2018, Chris Angelico <rosuav@gmail.com> wrote:
On Sat, Apr 28, 2018 at 6:06 AM, Wes Turner <wes.turner@gmail.com> wrote:
> On Friday, April 27, 2018, Chris Angelico <rosuav@gmail.com> wrote:
>> On Fri, Apr 27, 2018 at 8:18 PM, Wes Turner <wes.turner@gmail.com> wrote:
>> > IDK, I could just be resistant to change, but this seems like something
>> > that
>> > will decrease readability -- and slow down code review -- without any
>> > real
>> > performance gain. So, while this would be useful for golfed-down (!)
>> > one-liners with pyline,
>> > I'm -1 on PEP 572.
>> PEP 572 has never promised a performance gain, so "without any real
>> performance gain" is hardly a criticism.
>> > How do I step through this simple example with a debugger?
>> >
>> >     if re.search(pat, text) as match:
>> >         print("Found:", match.group(0))
>> Step the 'if' statement. It will call re.search() and stash the result
>> in 'match'. Then the cursor would be put either on the 'print' (if the
>> RE matched) or on the next executable line (if it didn't).
> Right. Pdb doesn't step through the AST branches of a line, so ternary
> expressions and list comprehensions and defining variables at the end of the
> line are 'debugged' after they're done.
> Similarly, code coverage is line-based; so those expressions may appear to
> be covered but are not.

I'm not sure I follow. In what situation would some code appear to be
covered when it isn't, due to an assignment expression?

When an assignment expression is in the else clause of a ternary expression, but the else clause does not execute because the condition is true, the assignment expression does not execute and so isn't covered.

if ((1) or (x := 3)):
if ((y := func(x)) if x else (x := 3))

Is this a new opportunity for misunderstanding?

Assignment expressions, though they are noticeable :=, may not actually define the variable in cases where that part of the line doesn't run but reads as covered.


Python-Dev mailing list
Unsubscribe: https://mail.python.org/mailman/options/python-dev/wes.turner%40gmail.com