[mypy] Fix type annotations for linked_stack.py

[archaengel]

$ mypy --ignore-missing-imports data_structures/stacks/linked_stack.py --strict
Success: no issues found in 1 source file

$ git checkout mypy-fix-stacks-linkedstack
Switched to branch 'mypy-fix-stacks-linkedstack'

$ mypy --ignore-missing-imports data_structures/stacks/linked_stack.py --strict
Success: no issues found in 1 source file

$ mypy --ignore-missing-imports data_structures/stacks --strict > after.txt

$ git checkout master
Switched to branch 'master'

$ mypy --ignore-missing-imports data_structures/stacks --strict > before.txt

$ diff before.txt after.txt
67,72d66
< data_structures/stacks/linked_stack.py:8: error: Function is missing a type annotation
< data_structures/stacks/linked_stack.py:12: error: Function is missing a return type annotation
< data_structures/stacks/linked_stack.py:49: error: Function is missing a return type annotation
< data_structures/stacks/linked_stack.py:55: error: Function is missing a return type annotation
< data_structures/stacks/linked_stack.py:66: error: Function is missing a return type annotation
< data_structures/stacks/linked_stack.py:99: error: Call to untyped function "Node" in typed context
85c79
< Found 82 errors in 12 files (checked 13 source files)
---
> Found 76 errors in 11 files (checked 13 source files)

Related to #4052

Describe your change:

Add generic type annotations for linked_stack.py.

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[poyea]

Thank you for your pull request!🤩

[archaengel]

Thanks for the review! 😸

[poyea]

ref: https://www.python.org/dev/peps/pep-0604/

[poyea]

So I guess #5577 is a doubly linked list implementation and this is a singly linked list implementation. How about we change #5577 to stack_with_doubly_linked_list.py and this to stack_with_singly_linked_list.py. Because when we generate directory, dll is not so helpful

[archaengel]

I think that makes sense. Should I open up a new PR for the rename or include those changes in with this one?

[poyea]

You can just make the changes here @archaengel

[archaengel]

Sgtm, done.

[archaengel]

@poyea Friendly bump 🙂