bpo-33499: Add PYTHONPYCACHEPREFIX env var for alt bytecode cache location. (GH-6834)

In some development setups it is inconvenient or impossible to write bytecode
caches to the code tree, but the bytecode caches are still useful. The
PYTHONPYCACHEPREFIX environment variable allows specifying an alternate
location for cached bytecode files, within which a directory tree mirroring the code
tree will be created. This cache tree is then used (for both reading and writing)
instead of the local `__pycache__` subdirectory within each source directory.

Exposed at runtime as sys.pycache_prefix (defaulting to None), and can
be set from the CLI as "-X pycache_prefix=path".

Patch by Carl Meyer.

1 files changed, 5 insertions, 0 deletions

diff --git a/Doc/library/compileall.rst b/Doc/library/compileall.rst
index 7b3963d..22d1c6b 100644
--- a/Doc/library/compileall.rst
+++ b/Doc/library/compileall.rst
@@ -109,6 +109,11 @@ There is no command-line option to control the optimization level used by the
 :func:`compile` function, because the Python interpreter itself already
 provides the option: :program:`python -O -m compileall`.
 
+Similarly, the :func:`compile` function respects the :attr:`sys.pycache_prefix`
+setting. The generated bytecode cache will only be useful if :func:`compile` is
+run with the same :attr:`sys.pycache_prefix` (if any) that will be used at
+runtime.
+
 Public functions
 ----------------