按需加载工作表xlrd1 1 0说明.pdfVIP

Docs » Loading worksheets on demand Loading worksheets on demand This feature, new in version 0.7.1, is erned by the on_demand argument to the open_workbook() func on and allows saving memory and me by loading only those sheets that the caller is interested in, and releasing sheets when no longer required. on_demand=False (default): No change. open_workbook() loads global data and all sheets, releases resources no longer mmap.mmap required (pr ipally the str or object containing the Workbook stream), and returns. on_demand=True and BIFF version 5.0: A warning message is emi ed, on_demand is recorded as False , and the old process is followed. on_demand=True and BIFF version = 5.0: open_workbook() loads global data and returns without releasing resources. At this stage, the only informa on available about sheets is Book.nsheets and Book.sheet_names() . Book.sheet_by_name() and Book.sheet_by_index() will load the requested sheet if it is not already loaded. Book.sheets() will load all unloaded sheets. The caller may save memory by calling Book.unload_sheet() when finished with the sheet. This applies irrespec ve of the state of on_demand . The caller may re-load an unloaded sheet by calling Book.sheet_by_name() or Book.sheet_by_index() , except if the required resources have been released (which will have happened automa cally when on_demand is false). This is the only case where an excep on will be raised. The caller may query the state of a sheet using Book.sheet_loaded() . Book.release_resources() may used to save memory and close any memory-mapped file before proceeding to examine already-loaded sheets. Once resources are released, no further sheets can be loaded. When using on-demand, it is advisable to ensure that Book.release_resources() is always cal