Adding json serializer

vcr/persisters/filesystem.py

@@ -0,0 +1,22 @@
+import tempfile
+import os
+
+class FilesystemPersister(object):
+    @classmethod
+    def _secure_write(cls, path, contents):
+        """
+        We'll overwrite the old version securely by writing out a temporary
+        version and then moving it to replace the old version
+        """
+        dirname, filename = os.path.split(path)
+        fd, name = tempfile.mkstemp(dir=dirname, prefix=filename)
+        with os.fdopen(fd, 'w') as fout:
+            fout.write(contents)
+            os.rename(name, path)
+
+    @classmethod
+    def write(cls, cassette_path, data):
+        dirname, filename = os.path.split(cassette_path)
+        if dirname and not os.path.exists(dirname):
+            os.makedirs(dirname)
+        cls._secure_write(cassette_path, data)