Python for Delphi Developers - Part 2

Python for Delphi
Developers (Part II)
Webinar by Kiriakos Vlahos (aka PyScripter)
and Jim McKeeth (Embarcadero)

Contents
•VarPyth
Using python libraries and objects in Delphi code
•Core libraries
•Visualization
•Machine Learning
Python based data analytics in Delphi applications
•TPythonThread
Running python scripts without blocking your GUI
Creating Python extension modules using Delphi
•WrapDelphi and WrapDelphiVCL units
Python GUI development using the VCL

VarPyth
• High-level access to python objects from Delphi code
• It also allows you to create common python objects (lists, tuples etc.)
• Uses custom variants
• No need to use the low-level python API or deal with python object reference
counting
• Small performance penalty
• Example
• ShowMessage(SysModule.version)
• Explore Demo25 and the VarPyth unit tests

VarPyth Demoprocedure TForm1.FormCreate(Sender: TObject);
begin
var np := Import('numpy');
var np_array: Variant :=
np.array(VarPythonCreate([1,2,3,4,5,6,7,8,9,10]));
PythonModule.SetVar('np_array’,
ExtractPythonObjectFrom(np_array));
end;
Python code:
from delphi_module import np_array
print("type(np_array) = ", type(np_array))
print("len(np_array) = ", len(np_array))
print("np_array = ", np_array)
res_array = np_array.copy()
for i in range(len(np_array)):
res_array[i] *= np_array[i]
print("res_array = ", res_array)
Output:
type(np_array) = <class 'numpy.ndarray'>
len(np_array) = 10
np_array = [ 1 2 3 4 5 6 7 8 9 10]
res_array = [ 1 4 9 16 25 36 49 64 81 100]
procedure TForm1.btnRunClick(Sender: TObject);
begin
GetPythonEngine.ExecString(UTF8Encode(sePythonCode.Text));
for var V in VarPyIterate(MainModule.res_array) do
ListBox.Items.Add(V);
end;
To learn more, explore Demo25 and the VarPyth unit tests

Core Python Libraries
• Core libraries
• numpy – arrays and matrix algebra
• scipy – math, science and engineering
• pandas – data structure and analysis, R-like dataframes
• Data visualization
• matplotlib – matlab-like plotting
• seaborn – statistical data visualization
• mpld3 – turn matplotlib plots into interactive web pages
• bokeh - interactive visualization library for modern browsers
• plotly – interactive browser-based graphing library
• altair – based on the visualization grammar vega-light

Data visualization
Demos - pyVIZsvg
• Create charts with python
libraries, save them in svg
format and plot them in Delphi
• Uses matplotlib and seaborn
python libraries
• Uses TSVGIconImage from
EtheaDev SVGIconImageList
components

Interactive Data
Visualization Demo -
PychartHtml
• Create interactive charts in
python save them to html and
show them inside Delphi
applications
• Showcases the new
TEdgeBrowser
• Uses the matplotlib with mpld3,
altair and bohek python
libraries

Machine Learning Python Libraries
• tensorflow (Google)
• keras – high level pythonic interface
• PyTorch (Facebook)
• CNTK - The Microsoft Cognitive Toolkit (Microsoft)
• Spark MLlib and mxnet (Apache Foundation)
• scikit-learn
• pure-python, general library, wide coverage, good choice for newcomers to
ML/AI

Data Analytics Demo:
COVID-19
• Demonstrates the combined use of numpy,
pandas, matplotlib and scikit-learn
• Use pandas to download Covid-19 confirmed
cases data from Web and aggregate it
• Use scikit-learn to
• Split the data into training and test sets
• Transform the data
• Define model (Bayesian Ridge Regression)
• Optimize model parameters
• Generate predictions
• Use matplotlib to compare actual vrs fitted test
data.

Running Python Scripts Without
Blocking Your Main Thread
• Python uses the infamous Global Interpreter Lock (GIL)
• This means that only one thread can run python code at any given time
• Python switches between python created threads automatically
• Applications using python need to acquire the GIL before running python
code and release it soon afterwards
• Welcome to TPythonThread
• TThread descendent
• Automatically acquires and releases the GIL

Python threads –
demo33
• Shows you how to
• use TPythonThread
• use new sub-interpreters
• synchronize with the main
thread
• interrupt running threads
with a keyboard interrupt
exception

Technical Aside I
• FPU Exception mask
• Delphi’s default FPU exception mask is different from most other Windows apps
• Incompatible with python libraries written in C or C++
• If you use numpy, scipy, tensorflow etc. you need to match the FPU mask they
expect to operate with
• PythonEngine.pas provides a function for doing that: MaskFPUExceptions
• Call MaskFPUExceptions(True) before python is loaded
• e.g. the initialization section of your main form
• See the P4D Wiki page for details

Technical Aside II
• Working with different python distributions:
• P4D makes a good effort to discover registered python distributions automatically
• But sometimes you want to use python distributions which are not registered
• One such case is when want to deploy your application bundled with python.
Python.org offers such a minimal distribution for applications embedding python.
• Additional considerations apply when using an Anaconda distribution
• Read the Finding Python P4D Wiki page carefully

P4D Python Extension Modules
• Python extension modules are dynamic link libraries that can be used by
python in a way similar to modules developed in python.
• They have ‘pyd’ extension.
• P4D makes it very easy to create extension modules that contain functions
and types developed in Delphi.
• These extension modules can be used by Python, independently of Delphi,
and can be packaged with setuptools and distributed through PyPi.

Python extension modules Demo
function PyInit_DemoModule: PPyObject;
//function exported by dll – initializes the module
begin
try
gEngine := TPythonEngine.Create(nil);
gEngine.AutoFinalize := False;
gEngine.UseLastKnownVersion := False;
// Adapt to the desired python version
gEngine.RegVersion := '3.8';
gEngine.DllName := 'python38.dll';
gModule := TPythonModule.Create(nil);
gModule.Engine := gEngine;
gModule.ModuleName := 'DemoModule';
gModule.AddMethod('is_prime', delphi_is_prime,
'is_prime(n) -> bool' );
gEngine.LoadDll;
except
end;
Result := gModule.Module;
end;
Python test module: test.py
from DemoModule import is_prime
from timeit import Timer
def count_primes(max_n):
res = 0
for i in range(2, max_n + 1):
if is_prime(i):
res += 1
return res
Command line:
> C:PythonPython38python test.py
Number of primes between 0 and 1000000 = 78498
Elapsed time: 0.29756570000000004 secs

Wrapping VCL as a Python
Extension Module I
• We can use the same approach to create an extension module wrapping
VCL
• Uses the WrapDelphi and WrapDelphiVCL units
• The whole of VCL (almost) is wrapped in 40 lines of code
• The generated Delphi.pyd file is only 5Mbs
• It can be uses to create VCL-based GUIs in python without needing Delphi
• A similar approach could be used to wrap FMX and create a multi-platform
python GUI library
• Unclear whether there are licensing restrictions in distributing such a file

Wrapping VCL as a Python
Extension Module II
unit uMain;
interface
uses PythonEngine;
function PyInit_Delphi: PPyObject; cdecl;
implementation
uses WrapDelphi, WrapDelphiVCL;
// similar to the previous extension module
TestApp.py
from Delphi import *
class MainForm(Form):
def __init__(self, Owner):
self.Caption = "A Delphi Form..."
self.SetBounds(10, 10, 500, 400)
self.lblHello = Label(self)
self.lblHello.SetProps(Parent=self, Caption="Hello World")
self.lblHello.SetBounds(10, 10, 300, 24)
self.OnClose = self.MainFormClose
def MainFormClose(self, Sender, Action):
Action.Value = caFree
def main():
Application.Initialize()
Application.Title = "MyDelphiApp"
f = MainForm(Application)
f.Show()
FreeConsole()
Application.Run()
main()
Command line:
> C:PythonPython38python .TestApp.py

Summary
• With Python for Delphi you can get the best of both worlds
• P4D makes it very easy to integrate Python into Delphi applications in RAD
way, thus providing access to a vast range of python libraries
• Expose Delphi function, objects, records and types to Python using low or
high-level interfaces (WrapDelphi)
• Create/Access/Use Python objects/modules in your Delphi code using a high-
level interface (VarPyth)
• Run python code in threads
• Create python extensions modules
• Wrap Vcl as a Python extension module to create GUIs with python
github.com/pyscripter/python4delphi/tree/master/Tutorials/Webinar%20II

Python for Delphi Developers - Part 2

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