Exception if opening workbook with unicode in formula
*Created originally on Bitbucket by [agellhaus (Arne Gellhaus)](https://bitbucket.org/%7B2e51ecdf-b5cc-4a3b-b462-218de4fa3a3b%7D/)* Exception: TypeError: expected <type 'str'> Could be fixed changing openpyxl\formatting\rule.py ``` #!python class Rule(...): formula = Sequence(expected_type=str) ``` to ``` #!python class Rule(...): formula = Sequence(expected_type=basestring) ```
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