Strange Index error on string formatting

[staticdev]

• Are you reporting a bug, or opening a feature request? Bug.
• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

import github # PyGithub
g = github.Github("access_token")
github_repo = "staticdev/git-portfolio"
repo = g.get_repo(github_repo)
try:
    created_pr = repo.create_pull(
        title="title", body="body", head="head", base="base", draft=False,
    )
except github.GithubException as github_exception:
    extra = ""
    for error in github_exception.data["errors"]:
        if "message" in error:
            extra += f"{error['message']} "
        else:
            extra += f"Invalid field {error['field']}. "

• What is the actual behavior/output?

src/git_portfolio/mypy.py:13:31: error: Invalid index type "str" for "Union[str, Dict[str, str]]"; expected type "Union[int, slice]"  [index]
                extra += f"{error['message']} "
                                  ^
src/git_portfolio/mypy.py:15:45: error: Invalid index type "str" for "Union[str, Dict[str, str]]"; expected type "Union[int, slice]"  [index]
                extra += f"Invalid field {error['field']}. "
                                                ^

• What is the behavior/output you expect?
  I expected no error, since I did not declare any type for f-strings, and these are strings.

• What are the versions of mypy and Python you are using?
  mypy v0.782 python 3.8.2

  Do you see the same issue after installing mypy from Git master?
  yes

• What are the mypy flags you are using? (For example --strict-optional)
  None.

[JelleZijlstra]

I haven't checked, but are you sure the f-strings are important here? This sounds to me like error is just of type Union[str, Dict[str, str]], and you'd get the same complaints from mypy whenever you try to index error with a string.

The error message is a bit weird though, since using an int or slice wouldn't work on the Dict part of the union either.

[staticdev]

@JelleZijlstra you are right, f-strings are not relevant here, I saw that after the test:

import github
g = github.Github("access_token")
github_repo = "staticdev/git-portfolio"
repo = g.get_repo(github_repo)
try:
    created_pr = repo.create_pull(
        title="title", body="body", head="head", base="base", draft=False,
    )
except github.GithubException as github_exception:
    extra = ""
    for error in github_exception.data["errors"]:
        if "message" in error:
            extra += "%s " % error['message']
        else:
            extra += "Invalid field %s. " % error['field']

Same error:

src/git_portfolio/mypy.py:13:36: error: Invalid index type "str" for "Union[str, Dict[str, str]]"; expected type "Union[int, slice]"  [index]
                extra += "%s " % error['message']
                                       ^
src/git_portfolio/mypy.py:15:51: error: Invalid index type "str" for "Union[str, Dict[str, str]]"; expected type "Union[int, slice]"  [index]
                extra += "Invalid field %s. " % error['field']
                                                      ^

I never came to these Index errors on mypy before. I don't understand why Union[int, slice] is expected here, I would expect str all the times in my code. And also this error cames from PyGithub GithubException data field:

class GithubException(Exception):
    @property
    def data(self) -> Dict[str, Union[str, List[str], List[Dict[str, str]]]]: ...

[Akuli]

string[bla] requires bla to be int or slice, as in "hello"[0] or "hello"[:3] (which is same as "hello"[slice(None, 3, None)])

possible workaround:

errors = cast(List[Dict[str, str]], github_exception.data["errors"])
for error in errors:
    ...

ideally GithubException.pyi would use a TypedDict (non-total if necessary)

[Akuli]

maybe this issue should be closed and you should instead make an issue to https://github.com/PyGithub/PyGithub ?

[staticdev]

@Akuli so your recommendation is create an issue asking them to use TypedDict?

[Akuli]

yes, ask them to use TypedDict or write documentation about how to access github_exception.data["errors"]

[staticdev]

@Akuli good I will create it today so we can close this one.

[staticdev]

Done @Akuli, closing this one. Thanks.