Add library_exists implementation (pandas-dev#661)

* add library_exists implementation

* updated library_exists() to work robustly without requiring auth

* fix typo for method name test_library_doesnt_exist

arctic/arctic.py

@@ -202,6 +202,34 @@ def list_libraries(self):
                         libs.append(coll[:-1 * len(self.METADATA_COLL) - 1])
         return libs
 
+    def library_exists(self, library):
+        """
+        Check whether a given library exists.
+
+        Parameters
+        ----------
+        library : `str`
+            The name of the library. e.g. 'library' or 'user.library'
+
+        Returns
+        -------
+        `bool`
+            True if the library with the given name already exists, False otherwise
+        """
+        exists = False
+        try:
+            # This forces auth errors, and to fall back to the slower "list_collections"
+            ArcticLibraryBinding(self, library).get_library_type()
+            # This will obtain the library, if no exception thrown we have verified its existence
+            self.get_library(library)
+            exists = True
+        except OperationFailure:
+            exists = library in self.list_libraries()
+        except LibraryNotFoundException:
+            pass
+        return exists
+
+
     @mongo_retry
     def initialize_library(self, library, lib_type=VERSION_STORE, **kwargs):
         """

tests/integration/test_arctic.py

@@ -1,8 +1,9 @@
 import pytest
 import time
 from datetime import datetime as dt
-from mock import patch
+from mock import patch, MagicMock
 from pandas.util.testing import assert_frame_equal
+from pymongo.errors import OperationFailure
 
 from arctic.arctic import Arctic, VERSION_STORE
 from arctic.exceptions import LibraryNotFoundException, QuotaExceededException
@@ -211,3 +212,19 @@ def test_lib_rename_namespace(arctic):
 def test_lib_type(arctic):
     arctic.initialize_library('test')
     assert(arctic.get_library_type('test') == VERSION_STORE)
+
+
+def test_library_exists(arctic):
+    arctic.initialize_library('test')
+    assert arctic.library_exists('test')
+    assert not arctic.library_exists('nonexistentlib')
+
+
+def test_library_exists_no_auth(arctic):
+    arctic.initialize_library('test')
+    with patch('arctic.arctic.ArcticLibraryBinding') as AB:
+        AB.return_value = MagicMock(
+            get_library_type=MagicMock(side_effect=OperationFailure("not authorized on arctic to execute command")))
+        assert arctic.library_exists('test')
+        assert AB.return_value.get_library_type.called
+        assert not arctic.library_exists('nonexistentlib')

tests/unit/test_arctic.py

@@ -329,7 +329,7 @@ def test_initialize_library_too_many_ns():
     assert 'Too many namespaces 5001, not creating: sentinel.lib_name' in str(e)
 
 
-def test_initialize_library():
+def test_initialize_library_with_list_coll_names():
     self = create_autospec(Arctic)
     self._conn = create_autospec(MongoClient)
     lib = create_autospec(ArcticLibraryBinding)
@@ -346,6 +346,18 @@ def test_initialize_library():
     assert lib_type.initialize_library.call_args_list == [call(ML.return_value, thing=sentinel.thing)]
 
 
+def test_library_exists():
+    self = create_autospec(Arctic)
+    self.get_library.return_value = 'not an exception'
+    assert Arctic.library_exists(self, 'mylib')
+
+
+def test_library_doesnt_exist():
+    self = create_autospec(Arctic)
+    self.get_library.side_effect = LibraryNotFoundException('not found')
+    assert not Arctic.library_exists(self, 'mylib')
+
+
 def test_get_library():
     self = create_autospec(Arctic)
     self._library_cache = {}