Debugging

Since xlwings runs in every Python environment, you can use your preferred way of debugging.

  • RunPython: When calling Python through RunPython, you can set a mock_caller to make it easy to switch back and forth between calling the function from Excel and Python.
  • UDFs: For debugging User Defined Functions, xlwings offers a convenient debugging server

To begin with, Excel will show Python errors in a Message Box:

_images/debugging_error.png

Note

On Mac, if the import of a module/package fails before xlwings is imported, the popup will not be shown and the StatusBar will not be reset. However, the error will still be logged in the log file. For the location of the logfile, see LOG_FILE default locations.

RunPython

Consider the following sample code of your Python source code my_module.py:

# my_module.py
import os
import xlwings as xw

def my_macro():
    wb = xw.Book.caller()
    wb.sheets[0].range('A1').value = 1

if __name__ == '__main__':
    # Expects the Excel file next to this source file, adjust accordingly.
    xw.Book('myfile.xlsxm').set_mock_caller()
    my_macro()

my_macro() can now easily be run from Python for debugging and from Excel via RunPython without having to change the source code:

Sub my_macro()
    RunPython ("import my_module; my_module.my_macro()")
End Sub

UDF debug server

Windows only: To debug UDFs, just set UDF_DEBUG_SERVER = True in the VBA Settings, at the top of the xlwings VBA module. Then add the following lines at the end of your Python source file and run it. Depending on which IDE you use, you might need to run the code in “debug” mode (e.g. in case you’re using PyCharm or PyDev):

if __name__ == '__main__':
    xw.serve()

When you recalculate the Sheet (Ctrl-Alt-F9), the code will stop at breakpoints or output any print calls that you may have.

The following screenshot shows the code stopped at a breakpoint in the community version of PyCharm:

_images/udf_debugging.png

Note

When running the debug server from a command prompt, there is currently no gracious way to terminate it, but closing the command prompt will kill it.