Add type checking

[jvasile]

In an ideal world, a codebase that receives inconsistent attention would have a full suite of tests, type checks, and sample files. Tests are time-consuming to write and will have to wait on sample files anyway. But type checks! We can do those. This issue is for making progress on getting the codebase to pass "mypy --strict" and we can do it one bit at a time.

Along the way, that will prompt changes that hopefully get us to a better place with consistency and return values and classes.

[radnonymous]

I thought I'd take a stab at this, posting this to make sure I'm on the right track.

~$ mypy /path/to/ots-bookkeeping --strict

yields

ots-bookkeeping/plugins/share_postings.py:54: error: Cannot find implementation or library stub for module named 'beancount'
ots-bookkeeping/plugins/share_postings.py:54: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
ots-bookkeeping/plugins/share_postings.py:55: error: Cannot find implementation or library stub for module named 'beancount.core'
ots-bookkeeping/plugins/share_postings.py:61: error: Cannot find implementation or library stub for module named 'beancount.parser'
ots-bookkeeping/plugins/share_postings.py:62: error: Cannot find implementation or library stub for module named 'beancount.query'
ots-bookkeeping/plugins/share_postings.py:67: error: Function is missing a type annotation
ots-bookkeeping/plugins/share_postings.py:119: error: Incompatible types in assignment (expression has type "Pattern[str]", variable has type "str")
ots-bookkeeping/plugins/share_postings.py:127: error: Need type annotation for 'sharees' (hint: "sharees: List[<type>] = ...")
ots-bookkeeping/plugins/share_postings.py:130: error: "str" has no attribute "finditer"
ots-bookkeeping/plugins/share_postings.py:167: error: Function is missing a type annotation
ots-bookkeeping/plugins/share_postings.py:183: error: Incompatible types in assignment (expression has type "Union[Tuple[Any, ...], List[Any]]", variable has type "List[str]")
ots-bookkeeping/plugins/share_postings.py:193: error: Call to untyped function "get_sharing_info" in typed context
ots-bookkeeping/plugins/share_postings.py:206: error: Call to untyped function "get_sharing_info" in typed context
Found 12 errors in 1 file (checked 2 source files)

I'm making a branch that will deal with these errors.
I'm guessing the first four issues are because I haven't given mypy access to beancount yet, so I'm going to disregard them for the time being.

[jvasile]

+1 to all of this, yeah.

Those first four might not be because mypy can't find beancount but rather because it can't find type information about beancount. This might be because there is none. In that case, we could add type info to beancount (a big project, but a useful one, and they want the changes upstream) or we could add "#type: ignore" to the "import beancount" line.

[jvasile]

I have been making some progress on this, and you can take a look at my recent commits to see what this work looks like in practice.