Valient's IT Notes

PostMessage vs. SendMessage

What is the difference between PostMessage and SendMessage?

PostMessage is asynchronous, sends a message in the message queue associated with the thread and returns without waiting for the thread to process that messaage.
SendMessage is synchronous, calls the window procedure for the specified window and does not return until the window procedure has processed the message.

For loop using an enumeration Example from Learning Embarcadero Delphi

Educational Example is from "Learning Embarcadero Delphi" - Free unaffiliated eBook created from Stack Overflow contributors.
The example is on RIP Tutorial - For loop using an enumeration
The code example will not be compiled in Embarcadero Delphi, gives out two error messages, one of them is:
"[dcc32 Error] EnumLoop.dpr(14): E2430 for-in statement cannot operate on collection type 'TWeekdays'"


program EnumLoop;

uses
  TypInfo;

type
  TWeekdays = (Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday);

var
  wd : TWeekdays;
begin

  for wd in TWeekdays do
    WriteLn(GetEnumName(TypeInfo(TWeekdays), Ord(wd)));

end.

The error explanation from docwiki Embarcadero

E2430 for-in statement cannot operate on collection type '%s' (Delphi) Go Up to Error and Warning Messages (Delphi) A for-in statement can only operate on the following collection types: Primitive types that the compiler recognizes, such as arrays, sets or strings Types that implement IEnumerable Types that implement the GetEnumerator pattern as documented in the Delphi Language Guide Ensure that the specified type meets these requirements.

To make the example to work, replace with this line:


for wd := Low(TWeekdays) to High(TWeekdays) do

The example was tested in CodeGear Delphi 2007, Embarcadero Delphi 10.4.2 Sydney, Embarcadero Delphi 11.3 Alexandria

Having worked through the book "Head First Python, 2nd Edition" by Paul Barry, released November 2016, I naively thought that I knew Python

Having worked through the book "Head First Python, 2nd Edition" by Paul Barry, released November 2016 (Publisher(s): O'Reilly Media, Inc.), I naively thought that I knew Python,

But when I started reading Mike McGrath Python in Easy Steps I realized that I don’t even know all the keywords of the Python language.


import keyword
for word in keyword.kwlist:
    print(word)

When one reaches the chapter — "Processing requests", there will be problems with Abyss Web Server, the settings made according to the official guide will not help: Adding Python Support.

All examples from the book work when leaving the page ".html" to ".py" page, parameters are passed and everything is displayed.

However, then suddenly everything stops working, even those examples that just worked, when trying to pass something from ".html" to ".py", Abyss Web Server gives the 500 error.

The record in the log: "AttributeError: partially initialized module 'cgi' has no attribute 'FieldStorage' (most likely due to a circular import)."

GUIs with Tkinter (and Fun with Turtles)

Turtle graphics is a popular way for introducing programming to kids. It was part of the original Logo programming language developed by Wally Feurzig and Seymour Papert in 1966.

The example that comes with the turtle docs:


from turtle import *

color('purple', 'cyan')
begin_fill()

while True:
    forward(200)
    left(170)
    if abs(pos()) < 1:
        break

end_fill()
done()

The example was found in the book "Head First Python, 2nd Edition" by Paul Barry, released November 2016, Publisher(s): O'Reilly Media, Inc.

Getting UserAgent and Browser name in Flask, Python

Inspired by the book "Head First Python, 2nd Edition" by Paul Barry, released November 2016, Publisher(s): O'Reilly Media, Inc.
where some examples don't work
Pages 296-300 of that book

Task 4: Create Code to Work with Our Webapp’s Database and Tables

Determine the Flask version.
First way: two lines in IDLE


 import flask 
 print(flask.__version__)

Second way: one command in Command line:


 pip show flask

The installed Flask version is uptodate - 3.0.3

Determine the Python version.
First way: two lines in IDLE


 from platform import python_version 
 python_version()

Second way: one command in Command line again:


 python -V

The installed Python version is uptodate too - 3.12.3

Coding in Python, Flask


 from flask import Flask 
 from flask import render_template, request

The method request.user_agent.browser returns nothing.
The next method requires one more importing


 from ua_parser import user_agent_parser

These three lines returns the browser name in browser variable:


 web_detail = str(request.user_agent) 
 user_browser = user_agent_parser.ParseUserAgent(web_detail) 
 browser = user_browser['family']

or briefer in single code line


 user_agent_parser.Parse(request.user_agent.string)['user_agent']['family']

I digress a little from the main trend of this note and give a method that receives all the User Agent:


 request.headers.get("user-agent")

Summing up, at the beginning, I believed the problem was that "request.user_agent.browser" did not return anything and found other methods to get the browser name. But still nothing was written to the database. I couldn't write to the field "browser_string" in the table "log" of the database "vsearchlogDB" anything, the value after insert operation was Null