Pylance shows a tuple of excepcions arent valid exception

[Durgeoble]

detected in the import from ftplib module all_errors.
Original code from ftplib.
# All exceptions (hopefully) that may be raised here and that aren't
# (always) programming errors on our side
all_errors = (Error, OSError, EOFError)

[erictraut]

Can you please provide a self-contained, minimal piece of code that reproduces the behavior? I'm not able to repro the problem from the screen shot above. Here's what I tried, and it seems to work fine:

all_errors = (OSError, EOFError)

def func():
    try:
        ...
    except all_errors as e:
        ...

I didn't include Error in the tuple because that isn't a standard built-in type, and I don't know how you have defined it.

[Durgeoble]

sure
language python
file ftplib # is a library but i put the relevant code

# Exception raised when an error or invalid response is received
class Error(Exception): pass
class error_reply(Error): pass          # unexpected [123]xx reply
class error_temp(Error): pass           # 4xx errors
class error_perm(Error): pass           # 5xx errors
class error_proto(Error): pass          # response does not begin with [1-5]
# All exceptions (hopefully) that may be raised here and that aren't
# (always) programming errors on our side
all_errors = (Error, OSError, EOFError)

file app.py

import ftplib  # the library from comes the code above
def dummyfuntion():
    try:
        print('do something')
    except ftplib.all_errors as e:
        raise

[jakebailey]

ftplib is a standard library module, and the tuple in question is defined here: https://github.com/python/typeshed/blob/b0c6598fbaccf92f15a8bc9c47934fd6276eaf78/stdlib/ftplib.pyi#L25

[erictraut]

OK, thanks for the additional details.

This appears to be a bug in the ftplib.pyi type stub. It defines all_errors as follows:

all_errors = Tuple[Type[Exception], ...]

In other words, it's defining all_errors as a type alias.

Based on the documentation, all_errors is not supposed to be a type alias; it's supposed to be a variable with the type Tuple[Type[Exception, ...]]. It should therefore be defined this way:

all_errors: Tuple[Type[Exception], ...]

I can submit a PR to the typeshed repo with this fix.

[jakebailey]

Wow, I completely missed that when I was looking at the stub.

[Durgeoble]

wow, so its a bug in the python library itself

[erictraut]

Here's the typeshed PR: python/typeshed#5271

[erictraut]

@Durgeoble, it's not a bug in the python library, but it is a bug in the typeshed stubs that describe the types used in the python library.

[erictraut]

Thanks to very quick turnaround from the maintainers of typeshed, the PR was already accepted and merged. I've pulled the latest typeshed stubs into the pyright repo, so the fix will be incorporated into an upcoming release of pylance.

Thanks again for the bug report.

[jakebailey]

This issue has been fixed in version 2021.5.0, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202150-5-may-2021