feat(pyarrow): add pyarrow suppport

This enables writing ladybug dataframes to parquet

close #2

ladybug_pandas/extension_types/arraytype.py

@@ -158,7 +158,6 @@ def _maybe_convert(arr):
 
 class LadybugArrayType(ExtensionArray, LadybugExtensionScalarOpsMixin):
 
-    # _dtype = LadybugDtype()
     _dtype = LadybugDType()
 
     def __init__(self, values, dtype=None, copy=False):
@@ -396,6 +395,11 @@ def __getitem__(self, item):
 
         return view
 
+    def __arrow_array__(self, type=None):
+        # convert the underlying array values to a pyarrow Array
+        import pyarrow as pa
+        return pa.array(self.data, type=pa.float64())
+
 
     def __len__(self) -> int:
         """
@@ -774,4 +778,4 @@ def astype(self, dtype, copy=True):
 
 
 LadybugArrayType._add_arithmetic_ops()
-LadybugArrayType._add_comparison_ops()
+LadybugArrayType._add_comparison_ops()

setup.py

@@ -20,6 +20,9 @@
     url="https://github.com/ladybug-tools/ladybug-pandas",
     packages=setuptools.find_packages(exclude=["tests"]),
     install_requires=requirements,
+    extras_require={
+        'arrow': ['pyarrow']
+    },
     classifiers=[
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: Implementation :: CPython",