Python GNUPG "sign+encrypt failed: Inappropriate ioctl for device" Within Docker Container

I can encrypt files perfectly fine when specifying a passphrase, but for some reason when I don't specify a passphrase, python-gnupg returns with:

`gpg: signing failed: Inappropriate ioctl for device`

I use a docker container for encrypting and decrypting.

I came across this Github issue (https://github.com/keybase/keybase-issues/issues/2798), which suggests to run:

`export GPG_TTY=$(tty)`

I've added this to my Dockerfile, but I'm still running into the same issue:

`RUN export GPG_TTY=$(tty)`

I couldn't find anything related to --no-tty in the docs (https://gnupg.readthedocs.io/en/latest/).

Any help with this would be appreciated!

Start by reproducing the sign-and-encrypt failure in the Docker container using python-gnupg, comparing runs with and without a passphrase. Read the linked GPG_TTY guidance, the Dockerfile command, and the python-gnupg documentation around --no-tty. Done means identifying a documented, reproducible configuration or a confirmed library issue.

Written by the indexing model from the issue text.