Re: [PATCH 4/4] scripts/qmp: Fix QEMU Python scripts path

[Markus Armbruster <armbru@redhat.com>]

John Snow <jsnow@redhat.com> writes:

> On 4/30/20 1:04 AM, Markus Armbruster wrote:
>> John Snow <jsnow@redhat.com> writes:
>> 
>>> On 4/21/20 5:42 AM, Philippe Mathieu-Daudé wrote:
>>>> QEMU Python scripts have been moved in commit 8f8fd9edba4 ("Introduce
>>>> Python module structure"). Use the same sys.path modification used
>>>> in the referenced commit to be able to use these scripts again.
>>>>
>>>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>>>> ---
>>>>  scripts/qmp/qmp      | 4 +++-
>>>>  scripts/qmp/qom-fuse | 4 +++-
>>>>  scripts/qmp/qom-get  | 4 +++-
>>>>  scripts/qmp/qom-list | 4 +++-
>>>>  scripts/qmp/qom-set  | 4 +++-
>>>>  scripts/qmp/qom-tree | 4 +++-
>>>>  6 files changed, 18 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/scripts/qmp/qmp b/scripts/qmp/qmp
>>>> index 0625fc2aba..8e52e4a54d 100755
>>>> --- a/scripts/qmp/qmp
>>>> +++ b/scripts/qmp/qmp
>>>> @@ -11,7 +11,9 @@
>>>>  # See the COPYING file in the top-level directory.
>>>>  
>>>>  import sys, os
>>>> -from qmp import QEMUMonitorProtocol
>>>> +
>>>> +sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..', 'python'))
>>>> +from qemu.qmp import QEMUMonitorProtocol
>>>>  
>>>
>>> Try to avoid using sys.path hacks; they don't work in pylint or mypy and
>>> it provides an active barrier to CQA work here.
>>> (They also tend to be quite fragile.)
>>>
>>> We can discuss the right way to do this; one of those ways is to create
>>> an installable package that we can install locally in a virtual environment.
>>>
>>> Another way is perhaps to set PYTHONPATH in the calling environment so
>>> that standard "import" directives will work.
>>>
>>> Both ultimately involve changing the environment of the user to
>>> accommodate the script.
>> 
>> For what it's worth, tests/Makefile.involve does the latter for
>> tests/qapi-schema/test-qapi.py.  Simple enough, but makes manual
>> invocation inconvenient.
>> 
>> Not necessary for scripts/qapi-gen.py, because its "import qmp.FOO"
>> finds qmp right in scripts/qmp/.
>> 
>
> Yes, using "proper" package hierarchies often means the loss of being
> able to invoke the scripts directly, unless you are careful to organize
> the package such that the scripts can run both in an "unpackaged" and a
> "packaged" mode.
>
> It can be done, but it's tricky and can be prone to error. Let's take a
> look at how to do it!
>
> Let's imagine we have an honest-to-goodness QAPI parser module. In
> isolation, the layout for such a package would probably look like this:
>
> qapi.git/
>   setup.py
>   qapi-gen.py
>   README.rst
>   qapi/
>     __init__.py
>     parser.py
>     schema.py
>     ...etc
>
>
> Now, anything inside of qapi/ is considered the "qapi module" and you
> will be unable to directly execute anything inside of this folder,
> unless it does not depend on anything else in the "qapi module".
>
> i.e. "import qapi.x" will work, but only from the executing context of a
> thread that understands how to find "qapi". If you are IN this
> directory, you do not have that context, so those directives will not work.
>
> Python imports are always handled relative to the importing file, not
> the imported file.
>
> qapi-gen in the parent directory, however, can use "from qapi import
> parser" without any problem, because if you are executing it directly,
> it will be able to see the "qapi module" as a folder.

Hmm...

    $ git-grep '^from.*schema' scripts/
    scripts/qapi-gen.py:from qapi.schema import QAPIError, QAPISchema
    scripts/qapi/events.py:from qapi.schema import QAPISchemaEnumMember
    scripts/qapi/gen.py:from qapi.schema import QAPISchemaVisitor
    scripts/qapi/introspect.py:from qapi.schema import (QAPISchemaArrayType, QAPISchemaBuiltinType,
    scripts/qapi/types.py:from qapi.schema import QAPISchemaEnumMember, QAPISchemaObjectType
    scripts/qapi/visit.py:from qapi.schema import QAPISchemaObjectType

How come importing from qapi. works in scripts/qapi/*.py, too?

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