course analytics error

/usr/bin/python3.7 /home/dmitry/PycharmProjects/Data_Analysis/example.py
Traceback (most recent call last):
  File "/home/dmitry/PycharmProjects/Data_Analysis/example.py", line 11, in <module>
    res2 = an.UseModule(1)
  File "/home/dmitry/PycharmProjects/Data_Analysis/Analisys/Analisys.py", line 22, in UseModule
    return _modules[id].Execute(_cursor, _courseName)
  File "/home/dmitry/PycharmProjects/Data_Analysis/Analisys/tests/main.py", line 36, in Execute
    avg = ta.calculateTests(df)
  File "/home/dmitry/PycharmProjects/Data_Analysis/Analisys/tests/content/tests_analisys.py", line 5, in calculateTests
    avg=df.groupby(['course_name','problem_id','page','attempts','max_grade'])['grade'].agg([np.mean, np.median, np.size])
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 3485, in aggregate
    (_level or 0) + 1)
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 3558, in _aggregate_multiple_funcs
    results[name] = obj.aggregate(func)
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 3489, in aggregate
    return getattr(self, cyfunc)()
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 1306, in mean
    return self._cython_agg_general('mean', **kwargs)
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 1056, in _cython_agg_general
    raise DataError('No numeric types to aggregate')
pandas.core.base.DataError: No numeric types to aggregate
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 63, in apport_excepthook
    from apport.fileutils import likely_packaged, get_recent_crashes
  File "/usr/lib/python3/dist-packages/apport/__init__.py", line 5, in <module>
    from apport.report import Report
  File "/usr/lib/python3/dist-packages/apport/report.py", line 30, in <module>
    import apport.fileutils
  File "/usr/lib/python3/dist-packages/apport/fileutils.py", line 23, in <module>
    from apport.packaging_impl import impl as packaging
  File "/usr/lib/python3/dist-packages/apport/packaging_impl.py", line 24, in <module>
    import apt
  File "/usr/lib/python3/dist-packages/apt/__init__.py", line 23, in <module>
    import apt_pkg
ModuleNotFoundError: No module named 'apt_pkg'

Original exception was:
Traceback (most recent call last):
  File "/home/dmitry/PycharmProjects/Data_Analysis/example.py", line 11, in <module>
    res2 = an.UseModule(1)
  File "/home/dmitry/PycharmProjects/Data_Analysis/Analisys/Analisys.py", line 22, in UseModule
    return _modules[id].Execute(_cursor, _courseName)
  File "/home/dmitry/PycharmProjects/Data_Analysis/Analisys/tests/main.py", line 36, in Execute
    avg = ta.calculateTests(df)
  File "/home/dmitry/PycharmProjects/Data_Analysis/Analisys/tests/content/tests_analisys.py", line 5, in calculateTests
    avg=df.groupby(['course_name','problem_id','page','attempts','max_grade'])['grade'].agg([np.mean, np.median, np.size])
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 3485, in aggregate
    (_level or 0) + 1)
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 3558, in _aggregate_multiple_funcs
    results[name] = obj.aggregate(func)
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 3489, in aggregate
    return getattr(self, cyfunc)()
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 1306, in mean
    return self._cython_agg_general('mean', **kwargs)
  File "/usr/local/lib/python3.7/dist-packages/pandas/core/groupby/groupby.py", line 1056, in _cython_agg_general
    raise DataError('No numeric types to aggregate')
pandas.core.base.DataError: No numeric types to aggregate

Process finished with exit code 1