ReadOnlyWorksheet.cell() raises an error.
*Created originally on Bitbucket by [slexbi (Alexander)](https://bitbucket.org/%7Beb984bc1-9273-47d5-9012-8a9a6ba35a5b%7D/)* ``` #!python wb0 = load_workbook('/home/myname/myfile.xlsx', read_only=True) ws0 = wb0['Sheet1'] ws0.cell(1, 1) TypeError: unbound method cell() must be called with Worksheet instance as first argument (got int instance instead) ws0.cell(ws0, 1, 1) TypeError: unbound method cell() must be called with Worksheet instance as first argument (got ReadOnlyWorksheet instance instead) ```
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