Introducing Python Backend Type Checks

[hardikkatehara]

Hi Oppia devs,

We are excited to say that our codebase now supports backend static type checks. This has been implemented by the PR #13060. These backend type checks will be added to pre-push hook in future through the PR #13114. When you merge with develop now, you should do the following:

• The developers will need to download python3.7 on their local systems. For downloading python3, please go through the Requirements for backend type checking.

Note: All the new backend files (with exceptions for some files/folders as mentioned in the wiki) are supposed to be type annotated, so please go through the Backend Type Annotations Wiki for more information on adding backend type annotations.