started work on backend

backend/venv/lib/python3.6/site-packages/pandas/api/__init__.py

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+""" public toolkit API """
+from . import types, extensions  # noqa

backend/venv/lib/python3.6/site-packages/pandas/api/extensions/__init__.py

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+"""Public API for extending panadas objects."""
+from pandas.core.accessor import (register_dataframe_accessor,  # noqa
+                                  register_index_accessor,
+                                  register_series_accessor)
+from pandas.core.algorithms import take  # noqa
+from pandas.core.arrays.base import ExtensionArray  # noqa
+from pandas.core.dtypes.dtypes import ExtensionDtype  # noqa

backend/venv/lib/python3.6/site-packages/pandas/api/types/__init__.py

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+""" public toolkit API """
+
+from pandas.core.dtypes.api import *  # noqa
+from pandas.core.dtypes.dtypes import (CategoricalDtype,  # noqa
+                                       DatetimeTZDtype,
+                                       PeriodDtype,
+                                       IntervalDtype)
+from pandas.core.dtypes.concat import union_categoricals  # noqa
+from pandas._libs.lib import infer_dtype  # noqa