CLN: added typing requirements for python 2.7. GH14468

CLN: created foundation for complex type annotations (GH14468)

This is mostly just a stub  file for now until a more clear picture develops

What has been noticed so far:

* numpy has no clear definition of what array_like means. all of these are valid:
   - Python scalars
   - tuples
   - lists
   - buffers
   - scalars in both python and numpy
   - more?
* similar story but not so extreme with dtypes
* python and numpy scalar helpers have been defined

CLN: annotated IndexOpsMixin (GH14468)

CLN: fixed a couple mistakes in IndexOpsMixin (GH14468)

CLN: cleaned up some import statements and reverted a file commited by accident (GH14468)

CLN: temporary work around for buffer error in python3 (GH14468)

CLN: temporary work around for buffer error in python3 part 2 (GH14468)

add trivial mypy check

Fixup

.travis.yml

@@ -50,7 +50,7 @@ matrix:
           - python-gtk2
     - os: linux
       env:
-        - JOB="3.5" TEST_ARGS="--skip-slow --skip-network" COVERAGE=true
+        - JOB="3.5" TEST_ARGS="--skip-slow --skip-network" COVERAGE=true TYPING=true
       addons:
         apt:
           packages:
@@ -116,6 +116,7 @@ script:
   - ci/script_single.sh
   - ci/script_multi.sh
   - ci/lint.sh
+  - ci/typing.sh
   - echo "script done"
 
 after_success:

ci/install_travis.sh

@@ -114,6 +114,10 @@ if [ "$LINT" ]; then
    pip install cpplint
 fi
 
+if [ "$TYPING" ]; then
+   pip install mypy-lang
+fi
+
 if [ "$COVERAGE" ]; then
     pip install coverage pytest-cov
 fi

ci/requirements-2.7.pip

@@ -6,3 +6,4 @@ py
 PyCrypto
 mock
 ipython
+typing

ci/typing.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+echo "inside $0"
+
+source activate pandas
+
+RET=0
+
+if [ "$TYPING" ]; then
+
+    echo "Typing  *.py"
+    mypy -2 pandas/core/base.py
+    if [ $? -ne "0" ]; then
+        RET=1
+    fi
+    echo "Typing *.py DONE"
+
+else
+    echo "NOT checking typing"
+fi
+
+exit $RET

pandas/core/algorithms.py

@@ -33,13 +33,18 @@
 from pandas.compat import string_types
 from pandas._libs import algos, lib, hashtable as htable
 from pandas._libs.tslib import iNaT
+import pandas.types.hinting as T  # noqa
+from pandas.core.dtypes.dtypes import ExtensionDtype  # noqa
 
 
 # --------------- #
 # dtype access    #
 # --------------- #
 
-def _ensure_data(values, dtype=None):
+def _ensure_data(values,     # type: T.ArrayLike
+                 dtype=None  # type: T.Optional[ExtensionDtype]
+                 ):
+    # type: (...) -> T.Tuple[T.ArrayLike, str, str]
     """
     routine to ensure that our data is of the correct
     input dtype for lower-level routines
@@ -130,6 +135,7 @@ def _ensure_data(values, dtype=None):
 
 
 def _reconstruct_data(values, dtype, original):
+    # type: (T.ArrayLike, str, str) -> T.ArrayLike
     """
     reverse of _ensure_data
 
@@ -156,6 +162,7 @@ def _reconstruct_data(values, dtype, original):
 
 
 def _ensure_arraylike(values):
+    # type: (T.Iterable) -> T.ArrayLike
     """
     ensure that we are arraylike if not already
     """
@@ -179,6 +186,7 @@ def _ensure_arraylike(values):
 
 
 def _get_hashtable_algo(values):
+    # type: (T.ArrayLike) -> T.Tuple(type, str, str)
     """
     Parameters
     ----------