x.subs(1/x,y) behavior differs when x is symbol and when x is a function solution by creating test_symbol_inverse.py #26446

[diya5722]

References to other Issues or PRs

Fixes #26446

Brief description of what is fixed or changed

In the code you provided, the main change compared to the old function is the addition of a check for whether old is a function using isinstance(old, Function). This check allows the code to differentiate between old being a symbol and old being a function, which is crucial for correctly handling the functional inverse in the substitution.

Other comments

Release Notes

NO ENTRY

[sympy-bot]

✅

Hi, I am the SymPy bot. I'm here to help you write a release notes entry. Please read the guide on how to write release notes.

• No release notes entry will be added for this pull request.

Click here to see the pull request description that was parsed.

<!-- Your title above should be a short description of what
was changed. Do not include the issue number in the title. -->

#### References to other Issues or PRs
Fixes #26446
<!-- If this pull request fixes an issue, write "Fixes #NNNN" in that exact
format, e.g. "Fixes #1234" (see
https://tinyurl.com/auto-closing for more information). Also, please
write a comment on that issue linking back to this pull request once it is
open. -->


#### Brief description of what is fixed or changed
In the code you provided, the main change compared to the old function is the addition of a check for whether old is a function using isinstance(old, Function). This check allows the code to differentiate between old being a symbol and old being a function, which is crucial for correctly handling the functional inverse in the substitution.

#### Other comments


#### Release Notes

<!-- Write the release notes for this release below between the BEGIN and END
statements. The basic format is a bulleted list with the name of the subpackage
and the release note for this PR. For example:

* solvers
  * Added a new solver for logarithmic equations.

* functions
  * Fixed a bug with log of integers. Formerly, `log(-x)` incorrectly gave `-log(x)`.

* physics.units
  * Corrected a semantical error in the conversion between volt and statvolt which
    reported the volt as being larger than the statvolt.

or if no release note(s) should be included use:

NO ENTRY

See https://github.com/sympy/sympy/wiki/Writing-Release-Notes for more
information on how to write release notes. The bot will check your release
notes automatically to see if they are formatted correctly. -->

<!-- BEGIN RELEASE NOTES -->
NO ENTRY
<!-- END RELEASE NOTES -->

[sympy-bot]

🟠

Hi, I am the SymPy bot. I've noticed that some of your commits add or delete files. Since this is sometimes done unintentionally, I wanted to alert you about it.

This is an experimental feature of SymPy Bot. If you have any feedback on it, please comment at sympy/sympy-bot#75.

The following commits add new files:

• 46ee69e:
  • sympy/core/mask_inverse_subs.py
• 0f425c7:
  • sympy/core/tests/test_symbol_inverse.py

The following commits delete files:

• 832befb:
  • sympy/core/mask_inverse_subs.py

If these files were added/deleted on purpose, you can ignore this message.

[1e9abhi1e10]

Please refer to this comment before making a new pull request.