def copy(self, old_name, new_name, index=None):
if index is None:<EOL><INDENT>index = len(self)<EOL><DEDENT>self._copy(old_name, new_name, index)<EOL>return self[new_name]<EOL>
Copies an old sheet with the old_name to a new sheet with new_name.

If an optional index argument is not provided then the created
sheet is appended at the end. Returns the new sheet.