ydb/contrib/tools/cython/COPYING.txt

The original Pyrex code as of 2006-04 is licensed under the following
license: "Copyright stuff: Pyrex is free of restrictions. You may use,
redistribute, modify and distribute modified versions."

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Cython, which derives from Pyrex, is licensed under the Apache 2.0
Software License.  More precisely, all modifications and new code
made to go from Pyrex to Cython are so licensed.

See LICENSE.txt for more details.

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The output of a Cython compilation is NOT considered a derivative
work of Cython.  Specifically, though the compilation process may
embed snippets of varying lengths into the final output, these
snippets, as embedded in the output, do not encumber the resulting
output with any license restrictions.