`flynt` breaks release pipeline

[95-martin-orion]

This line in setup.py generates a SyntaxError: invalid syntax in the release pipeline:

qsim/setup.py

Line 49 in 6c226ec

cmake_args += [f"-DCMAKE_LIBRARY_OUTPUT_DIRECTORY_{cfg.upper()}={extdir}"]

This was automatically formatted from the following by flynt:

qsim/setup.py

Lines 49 to 51 in 4912145

	cmake_args += [
	'-DCMAKE_LIBRARY_OUTPUT_DIRECTORY_{}={}'.format(cfg.upper(), extdir)
	]

It's unclear why this breaks the release, although it may be a backwards-compatibility issue.

[95-martin-orion]

Confirmed: f-strings are not supported before Python 3.6, and the release script was using Python 3.5.

Since we use f-strings elsewhere in the Python layer and Cirq already requires Python 3.6 or later, my preferred solution to this is to bump the Python requirement forward,

[95-martin-orion]

It turns out that the Kokoro machines that drive our release pipeline only have Python 3.5. Unless I can find a workaround to use Python 3.6 on those machines, we'll need to disable flynt in setup.py.

[95-martin-orion]

The v0.9.5 release provides a workaround by disabling flynt on setup.py. In the long term, we'll want to migrate our release pipeline over to Github Actions and re-enable flynt.