feat: Throw a more helpful exception when reading a closed part.

fixes #72

Author: defnull

multipart.py

@@ -884,6 +884,9 @@ def raw(self):
 
         Warning, this may consume a lot of memory, check :attr:`size` first.
         """
+        if self.file is None:
+            raise MultipartError("Cannot read from closed MultipartPart")
+
         pos = self.file.tell()
         self.file.seek(0)
 
@@ -895,6 +898,8 @@ def save_as(self, path):
         """ Save a copy of this part to `path` and return the number of bytes
             written.
         """
+        if self.file is None:
+            raise MultipartError("Cannot read from closed MultipartPart")
 
         with open(path, "wb") as fp:
             pos = self.file.tell()

test/test_legacy_parser.py

@@ -197,5 +197,12 @@ def test_segment_close(self):
         file1.close()
         self.assertIsNone(file1.file)
 
+        with self.assertMultipartError("Cannot read from closed MultipartPart"):
+            file1.raw
+        with self.assertMultipartError("Cannot read from closed MultipartPart"):
+            file1.value
+        with self.assertMultipartError("Cannot read from closed MultipartPart"):
+            file1.save_as("/tmp/foo")
+
         # Closing again is a NOP
         file1.close() # Do nothing