python/cpython

The sys.float_repr_style should be read-only

Opened this issue · 12 comments

skirpichev commented

Bug report

Bug description:

It's possible to "change" the repr style for floats:

Python 3.14.0a2+ (heads/long_export-decimal:4bb9ad04f5, Dec 17 2024, 05:39:57) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.float_repr_style
'short'
>>> sys.float_repr_style = 'legacy'
>>> sys.float_repr_style
'legacy'

Of course, this has no effect, as this variable just shows build-time settings. That certainly can misguide people, e.g. see this: #128005 (comment)

It could be nice to make this variable read-only (unfortunately, PEP 726 was rejected and it's might be not so easy). Or, at least, improve docs to mention that it's intended to be read-only (we emphasize this e.g. for int_info fields).

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

srinivasreddy commented

@skirpichev Are you working on it? Shall i take it?

srinivasreddy commented

So final resolution is to improve the docs that float_repr_style is only a read only field, and that any change to other values such as legacy has no effect on the formatting?

skirpichev commented

Are you working on it?

No. I'm not sure yet how it should be solved.

Shall i take it?

Sure.

So final resolution is to improve the docs that float_repr_style is only a read only field

The "problem" actually span not only this variable in the sys module. You can "change" everything:

>>> sys.maxsize
9223372036854775807
>>> sys.maxsize = 123
>>> sys.maxsize
123
>>> sys.int_info = "Spam"
>>> sys.int_info
'Spam'

Current docs looks ok for me. But it seems some people are misguided by such possibility. Maybe some generic note might help them.

vstinner commented

It could be nice to make this variable read-only

I don't think that we can easily solve this issue and I suggest to close it.

skirpichev commented

@vstinner, does it make sense for you as a documentation issue?

vstinner commented

Which kind of documentation addition are you thinking about? Add a note to each sys attribute? Add a global note to the sys module documentation?

skirpichev commented

Add a global note to the sys module documentation?

Yes, something like

diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index dd6293c722..1aedb277ef 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -8,7 +8,9 @@
 
 This module provides access to some variables used or maintained by the
 interpreter and to functions that interact strongly with the interpreter. It is
-always available.
+always available.  Except when explicitly noted otherwise, all variables are
+only for read access.
+
 
 
 .. data:: abiflags
vstinner commented

sys.path is a list and so is mutable. Does modifying sys.path content count as treating sys.path as read-only or not?

Well, sys.path doc says:

A program is free to modify this list for its own purposes.

skirpichev commented

And that fails to "when explicitly noted otherwise" :-) I'm not insist on exact wording as proposed above. Does it make sense for you?

vstinner commented

You can add this sentence if it matters to you:

Except when explicitly noted otherwise, all variables are only for read access.