New submission from Brian Skinn <bsk...@alum.mit.edu>:
doctest requires code examples have PS1 as ">>> " and PS2 as "... " -- that is,
each is three printed characters, followed by a space:
```
$ cat ell_err.py
import doctest
class Foo:
"""Test docstring.
>>>print("This is a test sentence.")
...a test...
"""
doctest.run_docstring_examples(
Foo(),
{},
optionflags=doctest.ELLIPSIS,
)
$ python3.8 --version
Python 3.8.0a3
$ python3.8 ell_err.py
Traceback (most recent call last):
...
ValueError: line 3 of the docstring for NoName lacks blank after >>>: '
>>>print("This is a test sentence.")'
$ cat ell_print.py
import doctest
class Foo:
"""Test docstring.
>>> print("This is a test sentence.")
...a test...
"""
doctest.run_docstring_examples(
Foo(),
{},
optionflags=doctest.ELLIPSIS,
)
$ python3.8 ell_print.py
Traceback (most recent call last):
...
ValueError: line 4 of the docstring for NoName lacks blank after ...: ' ...a
test...'
```
AFAICT, this behavior is consistent across 3.4.10, 3.5.7, 3.6.8, 3.7.3, and
3.8.0a3.
**However**, in this `ell_print.py` above, that "PS2" line isn't actually meant
to be a continuation of the 'source' portion of the example; it's meant to be
the *output* (the 'want') of the example, with a leading ellipsis to be matched
per `doctest.ELLIPSIS` rules.
The regex currently used to look for the 'source' of an example is
(https://github.com/python/cpython/blob/4f5a3493b534a95fbb01d593b1ffe320db6b395e/Lib/doctest.py#L583-L586):
```
(?P<source>
(?:^(?P<indent> [ ]*) >>> .*) # PS1 line
(?:\n [ ]* \.\.\. .*)*) # PS2 lines
\n?
```
Since this pattern is compiled with re.VERBOSE
(https://github.com/python/cpython/blob/4f5a3493b534a95fbb01d593b1ffe320db6b395e/Lib/doctest.py#L592),
the space-as-fourth-character in PS1/PS2 is not explicitly matched.
I propose changing the regex to:
```
(?P<source>
(?:^(?P<indent> [ ]*) >>>[ ] .*) # PS1 line
(?:\n [ ]* \.\.\.[ ] .*)*) # PS2 lines
\n?
```
This will then *explicitly* match the trailing space of PS1; it *shouldn't*
break any existing doctests, because the parsing code lower down has already
been requiring that space to be present in PS1, as shown for `ell_err.py` above.
This will also require an *explicit trailing space* to be present in order for
a line starting with three periods to be interpreted as a PS2 line of 'source';
otherwise, it will be treated as part of the 'want'. I made this change in my
local user install of 3.8's doctest.py, and it works as I expect on
`ell_print.py`, passing the test:
```
$ python3.8 ell_print.py
$
$ cat ell_wrongprint.py
import doctest
class Foo:
"""Test docstring.
>>> print("This is a test sentence.")
...a foo test...
"""
doctest.run_docstring_examples(
Foo(),
{},
optionflags=doctest.ELLIPSIS,
)
$ python3.8 ell_wrongprint.py
**********************************************************************
File "ell_wrongprint.py", line ?, in NoName
Failed example:
print("This is a test sentence.")
Expected:
...a foo test...
Got:
This is a test sentence.
```
For completeness, the following piece of regex in the 'want' section
(https://github.com/python/cpython/blob/4f5a3493b534a95fbb01d593b1ffe320db6b395e/Lib/doctest.py#L589):
```
(?![ ]*>>>) # Not a line starting with PS1
```
should probably also be changed to:
```
(?![ ]*>>>[ ]) # Not a line starting with PS1
```
I would be happy to put together a PR for this; I would plan to take a ~TDD
style approach, implementing a few tests first and then making the regex change.
----------
components: Library (Lib)
messages: 340788
nosy: bskinn
priority: normal
severity: normal
status: open
title: Tweak doctest 'example' regex to allow a leading ellipsis in 'want' line
type: enhancement
versions: Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue36714>
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