Use setup.py to install platform-specific dependencies#

For photos-to-sqlite I needed to install osxphotos as a dependency, but only if the platform is macOS - it’s not available for Linux.

Here’s the magic incantation to do that:

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setup(
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    name="photos-to-sqlite",
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    ...
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    install_requires=[
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        "sqlite-utils>=2.7",
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        "boto3>=1.12.41",
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        "osxphotos>=0.28.13 ; sys_platform=='darwin'",
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    ]
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)

So ; sys_platform=='darwin' in the install requires line.

More details: https://www.python.org/dev/peps/pep-0508/#environment-markers and https://hynek.me/articles/conditional-python-dependencies/