[Core] check if docker is installed if user_docker is specified.

[ekzhu]

Why are these changes needed?

Check if docker is installed if use_docker is specified. This is to adhere to the documentation of execute_code.

Related issue number

Address #498

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (871e9e2) 30.74% compared to head (c7c6b4e) 40.35%.

Files	Patch %	Lines
autogen/code_utils.py	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1145      +/-   ##
==========================================
+ Coverage   30.74%   40.35%   +9.60%     
==========================================
  Files          30       30              
  Lines        4043     4047       +4     
  Branches      915      965      +50     
==========================================
+ Hits         1243     1633     +390     
+ Misses       2721     2302     -419     
- Partials       79      112      +33     

Flag	Coverage Δ
unittests	40.27% <0.00%> (+9.58%)	⬆️

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[afourney]

So, this PR addresses the same issue that was meant to be addressed by the lines 280 - 291 in your code below. Issues #172 and #200 are where they were introduced.

At the time, the warning was added because we wanted to highlight the risk, but not change default behavior due to the installed user base. Perhaps it is now time to change this, and @sonichi can weigh in on this.

But, if we decide now to throw an error, we should remove lines 280-291, and we should update the docstring to mention that the error is thrown, and also update the description of the use_docker field, which now reads:

 use_docker (Optional, list, str or bool): The docker image to use for code execution.
            If a list or a str of image name(s) is provided, the code will be executed in a docker container
            with the first image successfully pulled.
            If None, False or empty, the code will be executed in the current environment.
            Default is None, which will be converted into an empty list when docker package is available.
            Expected behaviour:
                - If `use_docker` is explicitly set to True and the docker package is available, the code will run in a Docker container.
                - If `use_docker` is explicitly set to True but the Docker package is missing, an error will be raised.
                - If `use_docker` is not set (i.e., left default to None) and the Docker package is not available, a warning will be displayed, but the code will run natively.
            If the code is executed in the current environment,
            the code must be trusted.

And I believe that description is correct (though the language about an "empty" list is confusing)

[ekzhu]

Currently line 280-291 doesn't address the case when docker is not installed but use_docker is set to True. So technically the changes in this PR should address that case.

[afourney]

Currently line 280-291 doesn't address the case when docker is not installed but use_docker is set to True. So technically the changes in this PR should address that case.

Oh, ok. I see. Indeed you have provided a nicer error message.

Previously, If use docker was set to True, but Docker was not installed, then the code would throw an error here:

autogen/autogen/code_utils.py

Line 350 in 871e9e2

client = docker.from_env()

stating that docker was not defined.