[Python-ideas] Yield-from: Mysterious doctest failures

[Steven D'Aprano]

Greg Ewing wrote:
> I'm getting this from tests/test_generators.py. As far as
> I can see, the SyntaxError messages are identical. Does
> anyone know what doctest is complaining about here?
> 
> **********************************************************************
> File 
> "/Local/Projects/D/Python-YieldFrom/Python-2.6.1/Lib/test/test_generators.py", 
> line ?, in test.test_generators.__test__.coroutine
> Failed example:
>     def f(): x = yield = y
> Expected:
>     Traceback (most recent call last):
>       ...
>     SyntaxError: assignment to yield expression not possible (<doctest 
> test.test_generators.__test__.coroutine[23]>, line 1)
> Got:
>     Traceback (most recent call last):
>       File 
> "/Local/Projects/D/Python-YieldFrom/Python-2.6.1/Lib/doctest.py", line 
> 1231, in __run
>         compileflags, 1) in test.globs
>       File "<doctest test.test_generators.__test__.coroutine[22]>", line 1
>      SyntaxError: assignment to yield expression not possible (<doctest 
> test.test_generators.__test__.coroutine[22]>, line 1)
> ast: yield_expr: an = 0x10d9ed8
> **********************************************************************

The index in the coroutines are different: 23 expected, 22 got.

Also, unless it's an artifact of either your or my mail client, there's 
a spurious space *before* the SyntaxError exception. With spaces 
replaced by # for visibility:

Expected:
####Traceback (most recent call last):
######...
####SyntaxError: assignment to yield expression not possible (<doctest
test.test_generators.__test__.coroutine[23]>, line 1)

Got:
####Traceback (most recent call last):
######spam spam spam spam
#####SyntaxError: assignment to yield expression not possible (<doctest
test.test_generators.__test__.coroutine[22]>, line 1)

Assuming this is genuine, I have no idea how a SyntaxError exception 
ends up putting a space before the exception name!



-- 
Steven