Add __init__.py files in all the directories

[dhruvmanila]

Fixes: #2502

Please check if there's any directory where it's not needed.

Describe your change:

• Fix a bug or typo in an existing 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.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[TravisBuddy]

Travis tests have failed

Hey @dhruvmanila,
Please read the following log in order to understand the failure reason.
It'll be awesome if you fix what's wrong and commit the changes.

TravisBuddy Request Identifier: f7a588e0-017e-11eb-9be6-0d9634a5fbe7

[dhruvmanila]

That was a disaster! Let me see what's going on in there.

[dhruvmanila]

@cclauss Ok, I found the reason for all the errors.
The errors are happening because of how namespace packages work. As we're adding all the __init__.py files, we're basically creating sub-packages in our parent directory (Python/). What this means is that if we want to use import in a file inside a sub-directory, then we need to import using the dot notation or relative to the parent directory.

For example:
In ciphers/affine_cipher.py, instead of import cryptomath_module as cryptomath we will have to do import ciphers.cryptomath_module as cryptomath

This doesn't seem like a viable solution so I will take a further look into this.

[dhruvmanila]

I don't think there's any other choice if we're adding the __init__.py files.
It also seems that in some of the files we're using relative imports and in others we're using absolute. It would be better, in the long run, to stick with one. For more information on relative imports: https://docs.python.org/3/reference/import.html#package-relative-imports

If we're importing a module from the current directory we should use either relative or absolute imports and not just import module or from module import function:

• from parent.module import function
• from . import module
• from ..module import function
• import parent.module

Remember that a module is just another Python file.

[dhruvmanila]

I fixed all the imports on my local copy and it fixes everything up.
Shall I make a PR to fix the imports? @cclauss

[cclauss]

Yes. please. Just the changes required to get Travis CI to be ✅ again.

[AayushDadhich]

Typo

in data structures directory folder is named as trie instead of tree

[cclauss]

@AayushDadhich https://en.wikipedia.org/wiki/Trie