Add a __len__() function to doubly_linked_list.py

[Lakshmikanth2001]

Blocked by #2052

Describe your change:

in linked list class constructor i have added a data member called size and a function call length

• Add an algorithm?

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}.

[cclauss]

Please undo the maths/prime_check.py change and move that to a separate pull request as discussed in CONTRIBUTING.md.

[cclauss]

Blocked by #2052

[cclauss]

@Lakshmikanth2001 Thanks for this pull request because it found a flaw in doubly_linked_list.py. It would be great is you could fix that algorithm so that the tests in #2052 pass. If not, I will try to fix that at the end of this week. Thanks again.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

Please reopen this issue once you commit the changes requested or make improvements on the code. Thank you for your contributions.