Better types for modules

Open
#3,500 4 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
compilers, devtools

Research direction

Start by tracing mypy's handling of conditionally imported modules and how module types are joined across branches, using the random import and fastmath fallback examples as cases. Done means symbol-table information from each possible module is preserved so accesses such as fastmath.sin receive the appropriate inferred callable type.

Written by the indexing model from the issue text.

Description

feature needs discussion priority-2-low

In situations with dynamically/conditionally imported modules:

if random() > 0.5:
    import mod1
else:
    import mod2 as mod1

mypy can infer only types.ModuleType for the mod1 node. Another (quite widespread) example is something like:

try:
    import fastmath
except ImportError:
    import math as fastmath

In such case all symbol table information for math and fastmath is "lost". We could support (at least internally) some special type that will hold symbol table information and will be allowed to appear in unions (or support structural joins). For example, in the above case type of fastmath would be Union[Module['/path/to/fastmath'], Module['math']]. Then mypy will be able to infer fastmath.sin as Callable[[float], float].

Dominant language
Python
Stars
20.6k
Forks
3.3k
Avg merge
1d 18h
Merged PRs (30d)
54

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from python/mypy

All issues in python/mypy

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.