The functions are working for python 3.7 and sqlalchemy 1.3.5. Can we add tox configuration for them?

You can add the tox configs in this PR, then we also see right away whether the tests pass.

You can add the tox configs in this PR, then we also see right away whether the tests pass.

I have added tox config. All tests are passing.

Not sure if this is helpful at all, but I was just adapting this code for usage in our project, and had to use BytesIO to make it work. I'm using Python 3.8, sqlalchemy-schemadisplay==1.4.dev0, Pillow==7.0.0, pydot==1.4.1, ImageMagick 6.9.7-4 Q16 x86_64 20170114

@nhoening could you give more details on the issue? This PRs tests seem to work fine (which I didn't notice, thanks for updating @mayanksuman !)

Not sure what you need to know. I made this function (based on what I saw in this PR) in my script, and I had to use BytesIO, otherwise I got an error.

This is my function:

def show_image(*args, fb_viewer_command:str, kind:str, **kwargs):
    from io import BytesIO
    from PIL import Image
    print("Creating the pydot graph object...")
    if kind == "uml":
        g = create_uml_graph(*args, **kwargs)
    elif kind == "schema":
        g = create_schema_graph(*args, **kwargs)
    else:
        raise Exception(f"Cannot show image of kind {kind} ...")
    print("Creating PNG stream ...")
    iostream = BytesIO(g.create_png())
    print("Showing image ... (fallback viewer is %s)" % fb_viewer_command)
    Image.open(iostream).show(command=fb_viewer_command)

Here is the error I see if I use StringIO instead of BytesIO:

Traceback (most recent call last):
  File "../Common/src/datamodel/visualize_data_model.py", line 173, in <module>
    create_uml_pic(store=args.store)
  File "../Common/src/datamodel/visualize_data_model.py", line 111, in create_uml_pic
    show_image(mappers, **kwargs, fb_viewer_command=FALLBACK_VIEWER_CMD, kind="uml")
  File "../Common/src/datamodel/visualize_data_model.py", line 125, in show_image
    iostream = StringIO(g.create_png())
TypeError: initial_value must be str or None, not bytes

@nhoening have you tried to just use the fork directly?

No, I already installed 1.4.dev0 (master) for using restricted tables, didn't have time to pin to something more exotic. It works well for me now. If you guys think it's useful, I'll try it out if I ever have 15 minutes.

Referring to @mayanksuman 's opening comment, where he does mention BytesIO, maybe the tests only cover one kind of io, namely utf-8, which require StringIO? In any case, the error happens for me for both functions (schema and uml graphs) - I'm not expert enough to judge why I need BytesIO in my setup.

@abitrolly I now tried to call this fork's adapted function directly and I get the same error:

  File "src/datamodel/visualize_data_model.py", line 120, in create_uml_pic
    show_uml_graph(mappers, **kwargs)
  File "/home/nicolas/.local/share/virtualenvs/Common-aEUDK1MJ/lib/python3.8/site-packages/sqlalchemy_schemadisplay.py", line 220, in show_uml_graph
    iostream = StringIO(create_uml_graph(*args, **kwargs).create_png())
TypeError: initial_value must be str or None, not bytes

Making the same change as I did before (changing StringIO to BytesIO) makes it work again.

On my system, pydot.Dot().create_png() returns bytes. The docstring also says this (all create_* functions refer to create's docstring:

Creates and returns a binary image for the graph.

create will write the graph to a temporary dot file in the
encoding specified by `encoding` and process it with the
program given by 'prog' (which defaults to 'twopi'), reading
the binary image output and return it as:

- `str` of bytes in Python 2
- `bytes` in Python 3

I can successfully run pytest, so maybe the tests are not touching this code. I suggest someone writes a test for this function or tests this themselves on their machine.

@nhoening tox tests generate the coverage - you can see it in https://travis-ci.org/fschulze/sqlalchemy_schemadisplay/jobs/588254164#L252 You can look into the htmlcov dir in tox folder and see if this code is covered by tests or not.

It doesn't seem to me that the current tests are covering the issue I'm raising, see attached screenshot of my local tox session (using sqlalchemy-schemadisplay 1.4.dev0).

@mayanksuman while migrating from Travis to GitHub Actions in #28 and #29 I had to do the same code fixes that you did in this PR. Can you see if there is anything left in this PR or it can be closed? And thanks for the contribution anyway.

@nhoening it is better to reticket your issue that is not covered by tests, so that it can be addressed separately.

@abitrolly Just checked - I'm still using my own versions of show_uml_graph and show_schema_graph, where I use BytesIO, not StringIO.

I agree this can be a new ticket once I verified it still isn't working.

Do you guys have a version to test this with already that is later than 1.4dev0?

@nhoening I use this pyproject.toml syntax to install specific revisions from repository. But the problem is that PyPI doesn't allow to upload projects with such dependencies.

dependencies = [
  "sqlalchemy-schemadisplay @ https://github.com/fschulze/sqlalchemy_schemadisplay/archive/7c35dd35f07e55b2ed3880d62fcb4507152b7ac7.zip"
]

Thanks for the contribution, but I decided to go for the #35 as a fix for this.