ContextManagers: Add preserve_sys_path

coalib/misc/ContextManagers.py

@@ -3,6 +3,7 @@
 import os
 from io import StringIO
 import builtins
+import copy
 
 
 
@@ -82,3 +83,12 @@ def generate_input(self, x=''):
         yield input_generator
     finally:
         builtins.__dict__["input"] = _input
+
+
+@contextmanager
+def preserve_sys_path():
+    _path = copy.copy(sys.path)
+    try:
+        yield
+    finally:
+        sys.path = _path

coalib/tests/misc/ContextManagersTest.py

@@ -1,10 +1,12 @@
+import copy
 import unittest
 import sys
 
 sys.path.insert(0, ".")
 from coalib.misc.ContextManagers import (suppress_stdout,
                                          retrieve_stdout,
-                                         simulate_console_inputs)
+                                         simulate_console_inputs,
+                                         preserve_sys_path)
 
 
 class ContextManagersTest(unittest.TestCase):
@@ -41,6 +43,13 @@ def test_simulate_console_inputs(self):
             self.assertEqual(input(), 3)
             self.assertEqual(generator.last_input, 3)
 
+    def test_preserve_sys_path(self):
+        old_sys_path = copy.copy(sys.path)
+        with preserve_sys_path():
+            sys.path = 5
+
+        self.assertEqual(old_sys_path, sys.path)
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)