TL;DR: as of python 3.7, .pyc files by default include a timestamp and a size of the source file which results in a change of a hash every time a .pyc file is generated for a given source file. This results in staging conflicts for python parts. https://docs.python.org/3/library/py_compile.html#py_compile.compile https://docs.python.org/3/library/py_compile.html#py_compile.PycInvalidationMode.TIMESTAMP Even if this is set, there is still an issue https://github.com/pypa/pip/issues/8414 Description/analysis: When building a project with multiple identical python dependencies I consistently get an error like this: Failed to stage: Parts 'openstack-projects' and 'cluster' have the following files, but with different contents:     bin/activate     bin/activate.csh     bin/activate.fish     bin/python3     pyvenv.cfg     bin/python3     lib/python3.8/site-packages/Flask-1.1.2.dist-info/RECORD     lib/python3.8/site-packages/__pycache__/easy_install.cpython-38.pyc     lib/python3.8/site-packages/certifi/__pycache__/__init__.cpython-38.pyc     lib/python3.8/site-packages/certifi/__pycache__/__main__.cpython-38.pyc # many other .pyc files ... While snapcraft suggests that I use something like `organize`, `filesets` and `stage`, the issue is that the source files for those dependencies are identical - there is no reason for any manual work here. Source hashes are the same: snapcraft-microstack # sha256sum ./parts/cluster/install/lib/python3.8/site-packages/click/_textwrap.py 6a30b3933165cb9b639bd7e843937dfcc39e69824c063025b6e15aebd9f88976 ./parts/cluster/install/lib/python3.8/site-packages/click/_textwrap.py snapcraft-microstack # sha256sum ./parts/openstack-projects/install/lib/python3.8/site-packages/click/_textwrap.py 6a30b3933165cb9b639bd7e843937dfcc39e69824c063025b6e15aebd9f88976 ./parts/openstack-projects/install/lib/python3.8/site-packages/click/_textwrap.py .pyc files are different: snapcraft-microstack # sha256sum ./parts/openstack-projects/install/lib/python3.8/site-packages/click/__pycache__/_textwrap.cpython-38.pyc 398b47a5abfc87e9da73153e42d48dcd5d917bd637a0e0af1eb6999f19fb1085 ./parts/openstack-projects/install/lib/python3.8/site-packages/click/__pycache__/_textwrap.cpython-38.pyc snapcraft-microstack # sha256sum ./parts/cluster/install/lib/python3.8/site-packages/click/__pycache__/_textwrap.cpython-38.pyc d4642cfecd727d228944a1d31ff728e7ef6529a7a88898f6568ea6e96d1f8f82 ./parts/cluster/install/lib/python3.8/site-packages/click/__pycache__/_textwrap.cpython-38.pyc RECORD files include hashes as well, hence they are also different: snapcraft-microstack # diff ./parts/openstack-projects/install/lib/python3.8/site-packages/Flask-1.1.2.dist-info/RECORD ./parts/cluster/install/lib/python3.8/site-packages/Flask-1.1.2.dist-info/RECORD 1c1 < ../../../bin/flask,sha256=VXQqccMeG03Rn8_yN8Kq3Up13rzyaoHsEckFnCxHor4,242 --- > ../../../bin/flask,sha256=NAzPpe84iZFX3PYsCZEirt3fAFObAjBuCpM25792kSU,231 Apparently, as of python 3.7, .pyc files include a timestamp and a size of the source by default (PycInvalidationMode.TIMESTAMP). There is a way to override this behavior by setting the SOURCE_DATE_EPOCH environment variable to switch py_compile to using PycInvalidationMode.CHECKED_HASH: https://docs.python.org/3/library/py_compile.html py_compile.compile(file, cfile=None, dfile=None, doraise=False, optimize=-1, invalidation_mode=PycInvalidationMode.TIMESTAMP, quiet=0) invalidation_mode should be a member of the PycInvalidationMode enum and controls how the generated bytecode cache is invalidated at runtime. The default is PycInvalidationMode.CHECKED_HASH ***if the SOURCE_DATE_EPOCH environment variable is set***, otherwise ***the default is PycInvalidationMode.TIMESTAMP***. https://docs.python.org/3/library/py_compile.html#py_compile.PycInvalidationMode.TIMESTAMP TIMESTAMP The .pyc file includes the timestamp and size of the source file, which Python will compare against the metadata of the source file at runtime to determine if the .pyc file needs to be regenerated. https://docs.python.org/3/library/py_compile.html#py_compile.PycInvalidationMode.CHECKED_HASH CHECKED_HASH The .pyc file includes a hash of the source file content, which Python will compare against the source at runtime to determine if the .pyc file needs to be regenerated. Adding something like this seems to be needed:     build-environment:       - SOURCE_DATE_EPOCH: '1591640328' However, see https://bugs.launchpad.net/snapcraft/+bug/1882535/comments/2