Key errors in tools.results.calculate_mvgd_stats()

[gplssm]

Traceback

Traceback (most recent call last):
  File "/home/guido/miniconda3/envs/ding0_tmp/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 4736, in get_value
    return libindex.get_value_box(s, key)
  File "pandas/_libs/index.pyx", line 51, in pandas._libs.index.get_value_box
  File "pandas/_libs/index.pyx", line 47, in pandas._libs.index.get_value_at
  File "pandas/_libs/util.pxd", line 98, in pandas._libs.util.get_value_at
  File "pandas/_libs/util.pxd", line 83, in pandas._libs.util.validate_indexer
TypeError: 'str' object cannot be interpreted as an integer

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "example_analyze_single_grid_district.py", line 71, in <module>
    example_stats(filename)
  File "example_analyze_single_grid_district.py", line 43, in example_stats
    stats = results.calculate_mvgd_stats(nd)
  File "/home/guido/git/ding0_tmp/ding0/tools/results.py", line 587, in calculate_mvgd_stats
    lv_impedance += (G_lv.adj[path[i]][path[i+1]]['branch'].type['L_l'] * 1e-3 * omega * \
  File "/home/guido/miniconda3/envs/ding0_tmp/lib/python3.6/site-packages/pandas/core/series.py", line 1071, in __getitem__
    result = self.index.get_value(self, key)
  File "/home/guido/miniconda3/envs/ding0_tmp/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 4744, in get_value
    raise e1
  File "/home/guido/miniconda3/envs/ding0_tmp/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 4730, in get_value
    return self._engine.get_value(s, k, tz=getattr(series.dtype, "tz", None))
  File "pandas/_libs/index.pyx", line 80, in pandas._libs.index.IndexEngine.get_value
  File "pandas/_libs/index.pyx", line 88, in pandas._libs.index.IndexEngine.get_value
  File "pandas/_libs/index.pyx", line 131, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/hashtable_class_helper.pxi", line 1607, in pandas._libs.hashtable.PyObjectHashTable.get_item
  File "pandas/_libs/hashtable_class_helper.pxi", line 1614, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'L_l'

Note: it's already resolved in branch fix/#315-deviating-stats by commit feee3a3. But, this commit introduces two unwanted print statement. Therefore,

1. Cherry pick the commit into fix branch
2. Remove prints