ENH: Added support to pickle Transformer (#1060)

Author: snowman2

docs/history.rst

@@ -11,6 +11,7 @@ Latest
 - BUG: :func:`pyproj.datadir.get_data_dir` support for conda Windows (issue #1029)
 - ENH: warn when :meth:`pyproj.crs.CRS.to_wkt()`, :meth:`pyproj.crs.CRS.to_proj4()`, or :meth:`pyproj.crs.CRS.to_json()` returns None (issue #1036)
 - ENH: Added support for int-like strings and numpy dtypes (issues #1026 and #1835)
+- ENH: Added support to pickle :class:`pyproj.transformer.Transformer` (issues #1058)
 
 3.3.0
 -------

pyproj/transformer.py

@@ -15,7 +15,7 @@
 from dataclasses import dataclass
 from itertools import chain, islice
 from pathlib import Path
-from typing import Any, Iterable, Iterator, List, Optional, Tuple, Union, overload
+from typing import Any, Dict, Iterable, Iterator, List, Optional, Tuple, Union, overload
 
 from pyproj import CRS
 from pyproj._compat import cstrencode
@@ -310,6 +310,14 @@ def __init__(
         self._local.transformer = transformer_maker()
         self._transformer_maker = transformer_maker
 
+    def __getstate__(self) -> Dict[str, Any]:
+        return {"_transformer_maker": self._transformer_maker}
+
+    def __setstate__(self, state: Dict[str, Any]):
+        self.__dict__.update(state)
+        self._local = TransformerLocal()
+        self._local.transformer = self._transformer_maker()
+
     @property
     def _transformer(self):
         """

test/test_transformer.py

@@ -1,5 +1,6 @@
 import concurrent.futures
 import os
+import pickle
 from array import array
 from functools import partial
 from glob import glob
@@ -1534,3 +1535,18 @@ def test_transformer_source_target_crs__none():
     transformer = Transformer.from_pipeline("+init=ITRF2008:ITRF2000")
     assert transformer.source_crs is None
     assert transformer.target_crs is None
+
+
+def test_pickle_transformer_from_pipeline():
+    transformer = Transformer.from_pipeline("+init=ITRF2008:ITRF2000")
+    assert transformer == pickle.loads(pickle.dumps(transformer))
+
+
+def test_pickle_transformer_from_crs():
+    transformer = Transformer.from_crs(
+        "EPSG:4326",
+        "EPSG:2964",
+        always_xy=True,
+        area_of_interest=AreaOfInterest(-136.46, 49.0, -60.72, 83.17),
+    )
+    assert transformer == pickle.loads(pickle.dumps(transformer))