lib: Copy over existing DataFile class

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

lib/data.py

@@ -0,0 +1,52 @@
+# Copyright 2019 (c) Anna Schumaker.
+import os
+import pickle
+import xdg.BaseDirectory
+
+__resource = "emmental"
+if os.environ.get("EMMENTAL_TESTING"):
+    __resource = "emmental-testing"
+
+READ  = 'rb'
+WRITE = 'wb'
+
+emmental_data = xdg.BaseDirectory.save_data_path(__resource)
+
+class DataFile:
+    def __init__(self, path, mode):
+        self.path = os.path.join(emmental_data, path)
+        self.temp = os.path.join(emmental_data, f".{path}.tmp")
+        self.mode = mode
+        self.file = None
+
+    def __enter__(self):
+        if self.mode == WRITE:
+            self.file = open(self.temp, self.mode)
+        elif self.mode == READ and self.exists():
+            self.file = open(self.path, self.mode)
+        return self
+
+    def __exit__(self, exp_type, exp_value, traceback):
+        if self.file:
+            self.file.close()
+            self.file = None
+            if self.mode == WRITE:
+                os.rename(self.temp, self.path)
+        return True
+
+    def exists(self):
+        return os.path.exists(self.path)
+
+    def pickle(self, obj):
+        if self.file:
+            pickle.dump(obj, self.file, pickle.HIGHEST_PROTOCOL)
+
+    def remove(self):
+        if not self.file and self.exists():
+            os.remove(self.path)
+            return True
+        return False
+
+    def unpickle(self):
+        if self.file:
+            return pickle.load(self.file)

lib/test_data.py

@@ -0,0 +1,70 @@
+# Copyright 2019 (c) Anna Schumaker.
+from . import data
+import os
+import unittest
+import xdg.BaseDirectory
+
+xdg_data_home = xdg.BaseDirectory.xdg_data_home
+testing_data  = os.path.join(xdg_data_home, "emmental-testing")
+testing_file  = os.path.join(testing_data, "test.file")
+testing_temp  = os.path.join(testing_data, ".test.file.tmp")
+
+class TestDataModule(unittest.TestCase):
+    def setUp(self):
+        if os.path.exists(testing_file): os.remove(testing_file)
+
+    def test_dir(self):
+        self.assertEqual(data.emmental_data, testing_data)
+        self.assertTrue(os.path.exists(testing_data))
+        self.assertTrue(os.path.isdir(testing_data))
+        self.assertEqual(data.READ, 'rb')
+        self.assertEqual(data.WRITE, 'wb')
+
+    def test_data_file_init(self):
+        f = data.DataFile("test.file", data.READ)
+        self.assertEqual(f.path, testing_file)
+        self.assertEqual(f.temp, testing_temp)
+        self.assertFalse(f.exists())
+        self.assertEqual(f.mode, data.READ)
+        self.assertIsNone(f.file)
+
+        f = data.DataFile("test.file", data.WRITE)
+        self.assertEqual(f.temp, testing_temp)
+        self.assertFalse(f.exists())
+        self.assertEqual(f.mode, data.WRITE)
+        self.assertIsNone(f.file)
+
+    def test_data_file_read_write(self):
+        test = [ "test", "saving", "a", "list" ]
+        with data.DataFile("test.file", data.READ) as f:
+            self.assertIsNone(f.file)
+            f.pickle(test)
+            self.assertIsNone(f.unpickle())
+            self.assertFalse(f.remove())
+            self.assertTrue(f.exists())
+
+        with data.DataFile("test.file", data.WRITE) as f:
+            self.assertIsNotNone(f.file)
+            self.assertEqual(f.file.name, testing_temp)
+            self.assertFalse(f.exists())
+            self.assertTrue(os.path.exists(testing_temp))
+            f.pickle(test)
+            self.assertFalse(f.remove())
+            self.assertTrue(f.exists())
+
+        self.assertIsNone(f.file)
+        self.assertFalse(os.path.exists(testing_temp))
+        self.assertTrue(f.exists())
+
+        with data.DataFile("test.file", data.READ) as f:
+            self.assertIsNotNone(f.file)
+            self.assertEqual(f.file.name, testing_file)
+            lst = f.unpickle()
+            self.assertEqual(test, lst)
+            self.assertFalse(f.remove())
+            self.assertTrue(f.exists())
+
+        f = data.DataFile("test.file", data.READ)
+        self.assertTrue(f.remove())
+        self.assertFalse(f.exists())
+        self.assertFalse(f.remove())