When using the Python plugin and there's a problem installing a Python package, Snapcraft aborts with both a verbatim error message from pip as well as a long trace. There's 3 ways to get this to happen which go through the same code path which is why I'm filing one bug for it: - A package from index (PyPI) can't be installed. - The URL to a VCS branch can't be cloned. - An error occurs downloading via http(s) eg. HTTP 404. parts: foo: plugin: python python-packages: - <email address hidden>:kalikiana/does-not-exist.git#egg=ham - http://someserver.org/packages/MyPackage-3.0.tar.gz See below for abbreviated traces going through "Pip.download": Collecting pip Could not find a version that satisfies the requirement pip (from versions: ) No matching distribution found for pip Traceback (most recent call last): [...] File "/home/rumo/dev/snapcraft/snapcraft/plugins/_python/_pip.py", line 196, in _ensure_pip_installed self.download({'pip'}) [...] File "/usr/lib/python3.5/subprocess.py", line 581, in check_call raise CalledProcessError(retcode, cmd) Invalid requirement: '<email address hidden>:kalikiana/does-not-exist.git' It looks like a path. Does it exist ? Traceback (most recent call last): [...] File "/home/rumo/dev/snapcraft/snapcraft/plugins/_python/_pip.py", line 275, in download self._python_package_dir] + args, cwd=cwd) [...] File "/usr/lib/python3.5/subprocess.py", line 581, in check_call raise CalledProcessError(retcode, cmd) Collecting http://someserver.org/packages/MyPackage-3.0.tar.gz HTTP error 404 while getting http://someserver.org/packages/MyPackage-3.0.tar.gz Could not install requirement http://someserver.org/packages/MyPackage-3.0.tar.gz because of error 404 Client Error: Not Found for url: http://someserver.org/packages/MyPackage-3.0.tar.gz Could not install requirement http://someserver.org/packages/MyPackage-3.0.tar.gz because of HTTP error 404 Client Error: Not Found for url: http://someserver.org/packages/MyPackage-3.0.tar.gz for URL http://someserver.org/packages/MyPackage-3.0.tar.gz Traceback (most recent call last): [...] File "/home/rumo/dev/snapcraft/snapcraft/plugins/_python/_pip.py", line 275, in download self._python_package_dir] + args, cwd=cwd) [...] File "/usr/lib/python3.5/subprocess.py", line 581, in check_call raise CalledProcessError(retcode, cmd)