Loading xlsx in read_only mode yields giant sheet

[dmosberger]

Loading spreadsheet tst.xlsx with read_only=True results in tablib trying to construct a sheet with 1048576 rows, which can take a long time and/or exhaust available memory:

from openpyxl import load_workbook
wb=load_workbook(filename='tst.xlsx', read_only=True)
wb.active.max_row
1048576

with read_only=False, openpyxl returns the expected number of rows:

from openpyxl import load_workbook
wb=load_workbook(filename='tst.xlsx', read_only=False)
wb.active.max_row
4

Openpyxl has this comment about read-only mode:

Read-only mode relies on applications and libraries that created the file providing correct information about the worksheets, specifically the used part of it, known as the dimensions. Some applications set this incorrectly.

so it seems to me it'd be safer if tablib were to use read_only=False or are there other issues with doing that? If the latter is the case, would it be possible to provide a means to force a spreadsheet to be loaded with read-only turned off? Unfortunately, we don't have any control over the tool that's generating the "incorrect" files as they come from a third-party web site.

fix.diff.txt

[claudep]

I'd be reluctant to renounce on the read_only optimization due to bad third-party behavior. However, I think we could expose a read_only parameter for import_set and import_book methods. Feel free to prepare a patch for this.

[dmosberger]

Thanks for getting this resolved so quickly. Much appreciated!