Deferred loading of openpyxl.worksheet.datavalidation.DataValidation.cells
Created originally on Bitbucket by jusdino (Justin Frahm)
Changesets for this Pull Request have not been imported, because it had been already declined on Bitbucket. Marked as closed by the import user.
This change lets large workbooks with data validation set for entire columns to load in a reasonable amount of time. DataValidation.cells is not populated all at load_workbook. Instead, each DataValidation object only loads its cells when they are needed.
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