bpo-29708: Setting SOURCE_DATE_EPOCH forces hash-based .pyc files (GH-5200)

To support reproducible builds, the setting of of SOURCE_DATE_EPOCH triggers the py_compile module -- and by extension, compileall -- to forcibly compile with hash-based .pyc files. This eliminates the possibility of timestamp-based .pyc files which vary between builds.

1 files changed, 2 insertions, 0 deletions

diff --git a/Lib/py_compile.py b/Lib/py_compile.py
index a0f4defdce..16dc0a011f 100644
--- a/Lib/py_compile.py
+++ b/Lib/py_compile.py
@@ -112,6 +112,8 @@ def compile(file, cfile=None, dfile=None, doraise=False, optimize=-1,
     the resulting file would be regular and thus not the same type of file as
     it was previously.
     """
+    if os.environ.get('SOURCE_DATE_EPOCH'):
+        invalidation_mode = PycInvalidationMode.CHECKED_HASH
     if cfile is None:
         if optimize >= 0:
             optimization = optimize if optimize >= 1 else ''