Use relative imports in generated Python packages

[twosigmajab]

Description

Internally, generated Python code uses absolute imports that hard-code the assumption that users have the package installed top-level with a name like "swagger_server". For example, the following line results in the code from swagger_server import util being generated:

https://github.com/swagger-api/swagger-codegen/blob/62b93fc/modules/swagger-codegen/src/main/resources/flaskConnexion/controller.mustache#L6

This prevents users from putting the code in a directory with a more semantic name of their choosing, such as "gensrc".

If the generated code instead used relative imports, e.g. from .. import util in this case, then users would be free to move the code into a directory with a name of their choosing, or even nested in a subdirectory so they could import it as from gensrc.swagger_server import util, and then all the generated code's internal imports would still work.

Swagger-codegen version

Using 2.3.1 but believe this occurs in all versions, not a regression.

Steps to reproduce

swagger-codegen --input-spec api.yml \
    --output ./desired/subdirectory/on/my/python/path \
    --lang python-flask

Related issues/PRs

Only found it mentioned in a comment on a different PR ("change to the name will not fix the problem unfortunately, we need those relative imports"):
#6839 (comment)

Suggest a fix/enhancement

Use relative imports.

[twosigmajab]

(to reiterate, passing --model-package gensrc does not fix the problem as the generated code still does imports like from swagger_server import ...)

[qzmfranklin]

Same issue encountered here.

I was running swagger-codegen-cli v2.3.1 (downloaded from maven central) on gitea's swagger template:

# 'swagger' is my own wrapper around 'swagger-codegen-cli'.
swagger \
    generate -l python -i gitea/api_v1.json \
    -o gitea_python_client

Two problems:

1. It generates a folder gitea_python_client. But the top level python module inside is named swagger_client. I'd like to be able to change that name if I could.

2. The generated code is broken because of its use of absolute imports. For example, in file swagger_client/models/gpg_key.py LINE 19:

from swagger_client.models.gpg_key import GPGKey  # noqa: F401,E501

This causes the Module not found runtime error.
I have commented out that line and one other line that is similar in nature (as in mirandacong/gitea_python_client@fdc4591) and it worked.

[jupe]

I've same issue, it seems to affect only tests folder.

[subtleseeker]

Same issue encountered here.

I was running swagger-codegen-cli v2.3.1 (downloaded from maven central) on gitea's swagger template:

# 'swagger' is my own wrapper around 'swagger-codegen-cli'.
swagger \
    generate -l python -i gitea/api_v1.json \
    -o gitea_python_client

Two problems:

1. It generates a folder gitea_python_client. But the top level python module inside is named swagger_client. I'd like to be able to change that name if I could.
2. The generated code is broken because of its use of absolute imports. For example, in file swagger_client/models/gpg_key.py LINE 19:

from swagger_client.models.gpg_key import GPGKey  # noqa: F401,E501

This causes the Module not found runtime error.
I have commented out that line and one other line that is similar in nature (as in mirandacong/gitea_python_client@fdc4591) and it worked.

Is there any solution to the first problem, specifically, is there a way now to rename swagger_client while generation or maybe after generation?