.. meta::
    :description lang=en:
		xlSlim tries to determine the correct data type to pass to the Python code. Type hints help xlSlim where there is uncertainty.

Passing simple data types
=========================

xlSlim tries to determine the correct data type to pass to the Python code. Type hints help xlSlim where there is uncertainty.

Let's see how this works. This Python module contains functions that return the type of the argument `x` supplied to each function.

.. code-block:: python

	from datetime import datetime

	def echo_type(x):
		return repr(type(x))


	def echo_type_int(x: int) -> str:
		return repr(type(x))


	def echo_type_float(x: float) -> str:
		return repr(type(x))


	def echo_type_string(x: str) -> str:
		return repr(type(x))


	def echo_type_bool(x: bool) -> str:
		return repr(type(x))


	def echo_type_datetime(x: datetime) -> str:
		return repr(type(x))

.. note::
	All the Python code and Excel files shown are available from github in the `xlslim-code-samples`_ repo. I highly recommend downloading the samples from github. The Excel workbooks contain many tips and tricks.


.. _xlslim-code-samples: https://github.com/RusselWebber/xlslim-code-samples/archive/refs/heads/main.zip

Save the Python code as a new file on your PC. I saved the file in my Documents folder.

Open Excel and enter this :func:`RegisterPyModule` formula (amending the location to match where you saved the file): ::

	=RegisterPyModule("C:\Users\russe\Documents\passing_simple_data.py")
	
The functions are now available to use in Excel. 

Open the `echo_type()` function in the Function Wizard and notice how different types are passed to Excel.

.. image:: ../_static/passing_simple_data_echo_type.png
  :width: 400
  :alt: Echo argument type in Excel

Some experimentation will show that xlSlim does these conversions for simple data types passed to Python functions with no type hints:

.. list-table:: Data Type Conversions With No Type Hints
   :widths: 25 25
   :header-rows: 1

   * - Excel
     - Python
   * - integer
     - float
   * - double
     - float	 
   * - string
     - string
   * - bool
     - bool
   * - datetime
     - float
	 
That is not bad, but notice that integers and datetimes are not correct.

Adding Type Hints
-----------------

As usual, adding type hints helps xlSlim work better. In the Python module above the functions echo_type_int, echo_type_float, echo_type_string, echo_type_bool and echo_type_datetime all have type hints specifying the argument types.

Open the `echo_type_int()` function in the Function Wizard and notice how xlSlim is able to use the type hints to correctly pass an integer to the Python code.

.. image:: ../_static/passing_simple_data_echo_type_int.png
  :width: 400
  :alt: Echo int type in Excel

The same is true for dates, in fact xlSlim is now able to handle any valid Excel datetime representation.
  
.. image:: ../_static/passing_simple_data_echo_type_datetime.png
  :width: 400
  :alt: Echo datetime type in Excel
  
.. list-table:: Data Type Conversions With Type Hints
   :widths: 25 25
   :header-rows: 1

   * - Excel
     - Python
   * - integer
     - integer
   * - double
     - float	 
   * - string
     - string
   * - bool
     - bool
   * - datetime
     - datetime