Issue #21750: mock_open.read_data can now be read from each instance, as it

could in Python 3.3.

Lib/unittest/mock.py

@@ -2286,6 +2286,7 @@ def _iterate_read_data(read_data):
     for line in data_as_list:
         yield line
 
+
 def mock_open(mock=None, read_data=''):
     """
     A helper function to create a mock to replace the use of `open`. It works
@@ -2298,24 +2299,6 @@ def mock_open(mock=None, read_data=''):
     `read_data` is a string for the `read` methoddline`, and `readlines` of the
     file handle to return.  This is an empty string by default.
     """
-    def _readlines_side_effect(*args, **kwargs):
-        if handle.readlines.return_value is not None:
-            return handle.readlines.return_value
-        return list(_data)
-
-    def _read_side_effect(*args, **kwargs):
-        if handle.read.return_value is not None:
-            return handle.read.return_value
-        return ''.join(_data)
-
-    def _readline_side_effect():
-        if handle.readline.return_value is not None:
-            while True:
-                yield handle.readline.return_value
-        for line in _data:
-            yield line
-
-
     global file_spec
     if file_spec is None:
         import _io
@@ -2324,21 +2307,42 @@ def mock_open(mock=None, read_data=''):
     if mock is None:
         mock = MagicMock(name='open', spec=open)
 
-    handle = MagicMock(spec=file_spec)
-    handle.__enter__.return_value = handle
+    def make_handle(*args, **kwargs):
+        # Arg checking is handled by __call__
+        def _readlines_side_effect(*args, **kwargs):
+            if handle.readlines.return_value is not None:
+                return handle.readlines.return_value
+            return list(_data)
 
-    _data = _iterate_read_data(read_data)
+        def _read_side_effect(*args, **kwargs):
+            if handle.read.return_value is not None:
+                return handle.read.return_value
+            return ''.join(_data)
 
-    handle.write.return_value = None
-    handle.read.return_value = None
-    handle.readline.return_value = None
-    handle.readlines.return_value = None
+        def _readline_side_effect():
+            if handle.readline.return_value is not None:
+                while True:
+                    yield handle.readline.return_value
+            for line in _data:
+                yield line
 
-    handle.read.side_effect = _read_side_effect
-    handle.readline.side_effect = _readline_side_effect()
-    handle.readlines.side_effect = _readlines_side_effect
+        handle = MagicMock(spec=file_spec)
+        handle.__enter__.return_value = handle
 
-    mock.return_value = handle
+        _data = _iterate_read_data(read_data)
+
+        handle.write.return_value = None
+        handle.read.return_value = None
+        handle.readline.return_value = None
+        handle.readlines.return_value = None
+
+        handle.read.side_effect = _read_side_effect
+        handle.readline.side_effect = _readline_side_effect()
+        handle.readlines.side_effect = _readlines_side_effect
+        _check_and_set_parent(mock, handle, None, '()')
+        return handle
+
+    mock.side_effect = make_handle
     return mock