more tabxlsx documentation

tabxlsx.md

@@ -8,3 +8,81 @@ A number of output format options are available but less than the tabtotext.py m
 openpyx1 for tabtotext but it is possible to write simple tables
 just with Python's zip and xml.etree builtin modules. That is also
 faster.
+
+### import tabxlsx
+
+The tabxlsx.py script can be used as a library.
+
+* use `readFromXLSX("file.xlsx") -> data` to get data out of an Excel file
+* use `tabtextfileXLSX("file.xlsx") -> (data, headers)` to get data and header info
+* use `tabtoXLSX("file.xlsx", data, headers, selects)` to write data into an Excel file
+
+and there are generic function that allow to write CSV and Markdown tables. These will
+run the xlsx output/input when the filename endswith ".xlsx" or ".xls".
+
+* use `tabtextfile("file.csv") -> (data, headers)` to get data and header from csv files
+* use `tabtextfile("file.md") -> (data, headers)` to get it for markdown tables in text
+* use `print_tabtotext("file.csv", data, headers, selects)` to write a csv file
+* use `print_tabtotext("file.md", data, headers, selects)` for markdown tables
+* use `print_tabtotext("", data, headers, selects, defaultformat="csv")` to stdout
+
+The code itself mimics that of openpyxl. 
+* use `load_workbook(filename)` to get a `Workbook` data frame from a file
+* use `make_workbook(data, headers)`to create a `Workbook` from the provided data
+* use `Workbook.save(filename)` to save the data to an xlsx file
+
+The `headers` arguments defines the default order and formatting of the provided
+input data, which is `List[Dict[str, CellValue]]`, so each row does not have an
+implicit order. Using `["b:.2f", "a"]` shows the `"b"` values first formatted with
+two digits after the decimal point. Then `"a"` and then the rest.
+
+### run tabxlsx.py
+
+Use `tabxlsx.py --help` for the latest options when running the script as a command
+line tool. The first argument is usually some `data.xlsx` but it can also be `.csv`
+or `.md` file - the input parser gets selected from the file extension automatically.
+
+Additional arguments are the columns to be selected for output - being a subset of
+the data from the input file. Just like with `headers` each column can be formatted
+in the style of Python's `string.format()`.
+
+Use `"@csv"` to ensure output as CSV instead of the default markdown tables. For
+the markdown tables, the columns of each row have the same width mich makes the
+data easier to read. Alternative @-formats are available as well, e.g. `"@wide"`
+or `"@data"` with the latter being tab-seperated CSV.
+
+* use `./tabxlsx.py data.xlsx -o data.csv` # to convert from xlsx to csv
+* use `./tabxlsx.py data.csv -o data.xlsx` # to convert from csv to xslx
+* use `./tabxlsx.py data.xlsx @csv` # to show the xlsx data as csv lines
+* use `./tabxlsx.py data.xlsx a b @csv` # but only the input columns a and b
+* use `./tabxlsx.py data.xlsx b:2.f a` # format the b number for a 2-column table
+* use `./tabxlsx.py data.xlsx a --unique` # get one column out, remove duplicates
+
+
+### development
+
+The code is just a fraction of the `"tabtotext.py"` formatting engine. The main
+channel for distribution of that single `"tabxlsx.py"`script is via pypi.org. You
+can use `pip download tabxlsx` to download the latest script to any target system.
+
+* https://pypi.org/project/tabxlsx/
+
+As the script does not have any dependencies, it can be copied around as is. Feel
+free to integrate it into your own Python project. Note that there is also a
+`unittest`-based `"tabxlsx.tests.py"` code that can ensure backward-compatibility 
+if you start extending the tabxlsx code.
+
+* https://github.com/gdraheim/tabtotext
+* https://github.com/gdraheim/timetrack-odoo
+
+Have fun!
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