/usr/lib/python2.7/dist-packages/sage/symbolic/ is in sagemath-common 8.1-7ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/python2.7/dist-packages/sage/symbolic/__init__.py
/usr/lib/python2.7/dist-packages/sage/symbolic/all.py
/usr/lib/python2.7/dist-packages/sage/symbolic/assumptions.py
/usr/lib/python2.7/dist-packages/sage/symbolic/benchmark.py
/usr/lib/python2.7/dist-packages/sage/symbolic/callable.py
/usr/lib/python2.7/dist-packages/sage/symbolic/comparison.pxd
/usr/lib/python2.7/dist-packages/sage/symbolic/complexity_measures.py
/usr/lib/python2.7/dist-packages/sage/symbolic/constants.py
/usr/lib/python2.7/dist-packages/sage/symbolic/expression.pxd
/usr/lib/python2.7/dist-packages/sage/symbolic/expression_conversions.py
/usr/lib/python2.7/dist-packages/sage/symbolic/function.pxd
/usr/lib/python2.7/dist-packages/sage/symbolic/function_factory.py
/usr/lib/python2.7/dist-packages/sage/symbolic/getitem.pxd
/usr/lib/python2.7/dist-packages/sage/symbolic/integration/
/usr/lib/python2.7/dist-packages/sage/symbolic/integration/__init__.py
/usr/lib/python2.7/dist-packages/sage/symbolic/integration/external.py
/usr/lib/python2.7/dist-packages/sage/symbolic/integration/integral.py
/usr/lib/python2.7/dist-packages/sage/symbolic/maxima_wrapper.py
/usr/lib/python2.7/dist-packages/sage/symbolic/operators.py
/usr/lib/python2.7/dist-packages/sage/symbolic/random_tests.py
/usr/lib/python2.7/dist-packages/sage/symbolic/relation.py
/usr/lib/python2.7/dist-packages/sage/symbolic/ring.pxd
/usr/lib/python2.7/dist-packages/sage/symbolic/series.pxd
/usr/lib/python2.7/dist-packages/sage/symbolic/subring.py
/usr/lib/python2.7/dist-packages/sage/symbolic/substitution_map.pxd
/usr/lib/python2.7/dist-packages/sage/symbolic/tests.py
/usr/lib/python2.7/dist-packages/sage/symbolic/units.py