'MergedCell' object attribute 'comment' is read-only

Created originally on Bitbucket by piotrdab_ (Piotr Dąbrowski)

I have a problem with opening some file. Trying to open it with read_only=True finishes without any problems, but I need to have an info whether a cell/row/column is hidden and currently don't see any other way than to load the file with read_only=False. I've stripped any unnecessary for this issue content from the file and attached as a test_file.xlsx. The file contain only one merged cell and does not open properly.

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In [1]: from openpyxl import load_workbook                                                                          

In [2]: load_workbook('/home/piotr/Desktop/test_file.xlsx')                                                         
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-2-48edaf6f6504> in <module>
----> 1 load_workbook('/home/piotr/Desktop/test_file.xlsx')

~/miniconda3/envs/openpyxl/lib/python3.7/site-packages/openpyxl/reader/excel.py in load_workbook(filename, read_only, keep_vba, data_only, keep_links)
    310     reader = ExcelReader(filename, read_only, keep_vba,
    311                         data_only, keep_links)
--> 312     reader.read()
    313     return reader.wb

~/miniconda3/envs/openpyxl/lib/python3.7/site-packages/openpyxl/reader/excel.py in read(self)
    272         self.read_theme()
    273         apply_stylesheet(self.archive, self.wb)
--> 274         self.read_worksheets()
    275         self.parser.assign_names()
    276         if not self.read_only:

~/miniconda3/envs/openpyxl/lib/python3.7/site-packages/openpyxl/reader/excel.py in read_worksheets(self)
    233                 comment_sheet = CommentSheet.from_tree(fromstring(src))
    234                 for ref, comment in comment_sheet.comments:
--> 235                     ws[ref].comment = comment
    236 
    237             # preserve link to VML file if VBA

AttributeError: 'MergedCell' object attribute 'comment' is read-only

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In [4]: openpyxl.__version__                                                                                        
Out[4]: '2.6.2'

Attachments: test_file.xlsx