Skip to content

gh-85566: State interpreter var "_" in appendix of tutorial #21654

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 7 commits into
base: main
Choose a base branch
from
Open

gh-85566: State interpreter var "_" in appendix of tutorial #21654

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
d54f806
Create 2020-07-27-23-02-27.bpo-41394.BEos8A.rst
wyz23x2 Jul 28, 2020
815fad9
Update appendix.rst
wyz23x2 Jul 28, 2020
5c716e1
Added space around "+"
wyz23x2 Jul 28, 2020
49f1dfa
Remove trailing whitespace on line 39
wyz23x2 Jul 28, 2020
8d194a8
Update 2020-07-27-23-02-27.bpo-41394.BEos8A.rst
wyz23x2 Jul 28, 2020
d5a85d5
Update 2020-07-27-23-02-27.bpo-41394.BEos8A.rst
wyz23x2 Jul 28, 2020
1dc346c
Merge branch 'main' into master
skirpichev Apr 19, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
26 changes: 26 additions & 0 deletions Doc/tutorial/appendix.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,32 @@ Typing an interrupt while a command is executing raises the
:exc:`KeyboardInterrupt` exception, which may be handled by a :keyword:`try`
statement.

.. _tut-var:
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

What about something less generic / cryptic:

Suggested change
.. _tut-var:
.. _tut-underscore-variable:


Special ``_`` variable
-------------------------

There is a special variable ``_`` in interactive mode, which stores the result of the last
evaluated expression. If the last expression evaluated to ``None``, then the value of ``_``
Comment on lines +61 to +62
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I'm thinking the two commas here are somewhat superfluous. What do you think?

Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Some grepping:

sk@note:~/src/cpython $ git grep '[[:space:]]`None' Doc/  # no hits
sk@note:~/src/cpython $ git grep -F '``None``' Doc/|wc -l
1396

is not updated.
Comment on lines +61 to +63
Copy link
Contributor

@skirpichev skirpichev Apr 19, 2025 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
There is a special variable ``_`` in interactive mode, which stores the result of the last
evaluated expression. If the last expression evaluated to ``None``, then the value of ``_``
is not updated.
There is a special variable ``_`` in interactive mode, which is updated with the result
of the last evaluated expression, unless it was ``None``.

Copy link
Member

@merwok merwok Apr 22, 2025 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I think the verb should be in the past: unless it was None

but would like a native speaker to confirm!


For example:

>>> _ # Not defined yet
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
_
NameError: name '_' is not defined
Comment on lines +66 to +71
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
>>> _ # Not defined yet
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
_
NameError: name '_' is not defined
.. doctest::
:options: +SKIP
>>> _ # Not defined yet
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
_
NameError: name '_' is not defined

I doubt this example is fixable. Either you could remove one or exclude entire block from testing, as suggested.

>>> 1 + 2
3
>>> _
3
>>> print("1+2=3")
1+2=3
>>> _ # Doesn't store None returned by print()
3
>>> _ + 4
7

.. _tut-scripts:

Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Documentation/2020-07-27-23-02-27.bpo-41394.BEos8A.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Added "Special ``_`` Variable" section to the "16. Appendix" part of Python tutorial.

It includes the define of ``_`` and an example.
Comment on lines +1 to +3
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
Added "Special ``_`` Variable" section to the "16. Appendix" part of Python tutorial.
It includes the define of ``_`` and an example.
Added "Special ``_`` Variable" section to the "16. Appendix" part of Python tutorial.

Loading