prevent writing duplicates

Author: minggli

pandas/io/common.py

@@ -437,7 +437,8 @@ def __init__(self, file, mode='r', **kwargs):
         super(BytesZipFile, self).__init__(file, mode, **kwargs)
 
     def write(self, data):
-        super(BytesZipFile, self).writestr(self.filename, data)
+        if self.filename not in self.nameslist():
+            super(BytesZipFile, self).writestr(self.filename, data)
 
 
 class MMapWrapper(BaseIterator):