‘Type here to search’ suddenly stopped this morning on all of my virtual machines. Presumed this was a Parallels problem, however it’s related to Bing and lots of people have this problem…
The howtogeek page: https://www.howtogeek.com/224159/how-to-disable-bing-in-the-windows-10-start-menu/
My video…
Just discovered f-strings for Python string interpolation – much, much better than any of the other formatting techniques such as .format or %.
Example:
print(f'{name} is {age} years old')
Jon is 21 years old
I’ve written a load of examples and notes in an interactive Jupiter notebook, mainly for my own reference:
https://gitlab.com/cds/pythonlearning/blob/master/fstring.ipynb
It took a few attempts to get a compatible Python and OpenCV library running under Visual Studio Code on macOS Catalina using a virtual environment. I made a video to show how I got this going – this post just adds some more details.
There is also an excellent tutorial from Microsoft:
Getting Started with Python in VS Code
Visual Studio Code running on a virtual machine may have problems rendering the interface. This seems to be related to the underlying Electron framework and GPU acceleration. I made a quick video to show how I got around this:
A virgin Mac comes with Python 2.7 installed – this is not recommended and V3.7.5 works with OpenCV4 on a Mac. V3.8 does not work at the time of writing (although since I started writing this post it looks like it now does). Download the installer from the main python website by selecting Downloads, Mac OS X, and then selecting the 64-bit installer:
Run the installer – I used all default settings.
Download the installer from Visual Studio Code and immediately move the downloaded file to the Applications folder. (This is the actual application, not an installer). Try to run once – macOS will refuse due to security:
Close the message, open System Preferences, and select the Security and Privacy settings. Then select “Open Anyway” to allow VSC.
Visual Studio Code should now start:
Open a folder by selecting Open folder and then add a new file. Save the file using the .py extension:
Visual Studio Code immediately offers to install the Python extension, select Install:
On a virgin Mac there will now be a prompt to install command line developer tools, so click Install if prompted and allow the installation to complete before returning to Visual Studio Code.
The status bar will show the selected interpret if everything has gone well:
Install the linter (pylint): this helps analyse the code for bugs and style issues. It also might not work first time but we can fix shortly…
If the terminal window suggests upgrading pip, the Python package manager, then go for it by running the following in the terminal window:
python3 -m pip install --upgrade pip
A virtual environment is a self-contained directory tree that contains a Python installation for a particular version of Python
https://docs.python.org/3/tutorial/venv.html
Each project can use its own virtual environment to ensure any modules it requires don’t clash with modules in other projects.
From the terminal create a virtual environment:
python3 -m venv .venv
Visual Studio Code will detect this new environment and offer to select it for the current project folder – select Yes:
Because this is a new Python environment you may need to install the linter again:
Now – the bit that confused me… the project is now using the .venv virtual environment:
However, the terminal session has so far only created the environment, it has not activated it for itself. The shell identifier says:
jon@Jons-MacBook-Pro Python %
There are two ways to fix this. First, using the source command in the terminal window:
source .venv/bin/activate
Second, by creating a new Terminal session using the command palette. (Select View, ten Command Palette):
Now the terminal shows that it’s using the virtual environment:
At last we can install OpenCV. Using the terminal session in the virtual environment we can first search for OpenCV packages:
python3 -m pip search opencv
When called with
https://docs.python.org/3/using/cmdline.html-m module-name, the given module is located on the Python module path and executed as a script
We see results like this:
opencv-utils (0.0.2) – OpenCV Utilities
ctypes-opencv (0.8.0) – ctypes-opencv – A Python wrapper for OpenCV using ctypes
opencv-wrapper (0.2.3) – A Python wrapper for OpenCV.
opencv-cython (0.4) – An alternative OpenCV wrapper
dajngo-opencv (0.3) – Django Opencv integratio
opencv-python (4.1.2.30) – Wrapper package for OpenCV python bindings
For this test I’m using opencv-python. The details on version 4.1.2.30 can be found on the Python Package Index site. Interestingly this version was only released a few hours ago and says it supports Python 3.8 😬 I guess I’ll try this on a virtual machine first to check it’s all ok!
Install OpenCV using pip:
python3 -m pip install opencv-python
First test: import the OpenCV module and print the library version.
import cv2
print('Using OpenCV version {0}'.format(cv2.__version__))
After running this output is shown in the terminal:
But – there’s a problem. In the editor the linter is suggesting that cv2 is not a known module:
This has been seen before on the pylint GitHub issues page. For me, the solution is to edit the .vscode settings. Using ⇧⌘E (shift+command+E) to view the explorer page, expand the .vscode file and click settings.json:
Add a comma to the end of the line of the existing setting, then add the following new setting:
"python.linting.pylintArgs": ["--generate-members"]
My settings now look like this:
And now the red squiggle has gone from cv2.__version__ 😀
All that remains is to learn Python and OpenCV which will surely lead to great things!
Hope this helps.
Apple trackpads, both external and built-in, have one fantastic gesture which is not enabled by default:
3 finger drag
https://support.apple.com/en-us/HT204609
This allows you to easily grab windows and files without needing to hold down the trackpad like a mouse button. For GUI designers it means quickly resizing and positioning controls, like Tom Cruise in Minority Report 😎
Tested with Parallels Desktop 15 Pro Edition on macOS Catalina.
Problem 1: using Visual Studio or notepad++ or any similar multi-document application in Windows 10 on a Mac using Parallels, ⌘W (Command+W) maps to Alt+F4. This means To close just an editor page you have to revert to the original Windows shortcut of Control+F4 which is a minor pain on a Mac with the Touch Bar instead of function keys.
Solution 1: change the Parallels preferences to remap ⌘W to Ctrl+F4. ⌘Q will still close an application but ⌘W will now close an internal editor window; this is the same behaviour used in Safari to close the whole application (⌘Q) or close just one page (⌘W).
Problem 2: Control+Tab and Shift+Control+Tab don’t switch between editor windows.
Solution 2: a recent update to Parallels resulted in these shortcuts being used for Parallels tab switching. They don’t get passed on to the VM. Just unchecking these shortcuts fixes the problem.
While running one of my apps on a Windows 10 VM I noticed that the timing was much different to that seen on the host PC. After lots of digging I finally found that the granularity of the system timer on the VM was around 16ms versus around 0.5ms on the host PC. My app is using some 1-5 millisecond sleeps but when the granularity is 16ms then 1ms becomes 16! (The actual granularity is 15.6ms due to a default 64Hz timer frequency).
Some cool resources on the web related to this:
Solved my problems by setting the granularity to the minimum supported by the PC; this setting remains in place until the application exits. So it just seems that my VM doesn’t have anything running that would otherwise cause the timer to run more quickly than the default (of 64Hz), whereas my development PC must have all sorts that are running the timer flat out; probably one reason my battery goes down more quickly than expected!
To query and change the granularity I used theses methods via C#:
I then wrote a little wrapper class to let me play with the timings using the .Net TimeSpan. Note: this is a frustrating struct to use because it really doesn’t want to use fractions of a millisecond without more than a bit of persuasion, specifically because FromMilliseconds will only consider the requested value to the nearest millisecond.
/// <summary>
/// Utility to query the timer resolution
/// </summary>
class TimerResolution
{
[DllImport("ntdll.dll", SetLastError = true)]
private static extern int NtQueryTimerResolution(out int MinimumResolution, out int MaximumResolution, out int CurrentResolution);
[DllImport("ntdll.dll", SetLastError = true)]
private static extern int NtSetTimerResolution(int DesiredResolution, bool SetResolution, out int CurrentResolution);
private static TimeSpan TimeSpanFrom100nsUnits(int valueIn100nsUnits)
{
var nanoseconds = (double)valueIn100nsUnits * 100.0;
var seconds = nanoseconds / 1000000000.0;
var ticks = seconds * System.Diagnostics.Stopwatch.Frequency;
var timeSpan = TimeSpan.FromTicks((long)ticks);
return timeSpan;
}
private static (TimeSpan min, TimeSpan max, TimeSpan cur) Query()
{
NtQueryTimerResolution(out var min, out var max, out var cur);
return (min: TimeSpanFrom100nsUnits(min), max: TimeSpanFrom100nsUnits(max), cur: TimeSpanFrom100nsUnits(cur));
}
/// <summary>Gets the minimum timer resolution</summary>
public static TimeSpan MinResolution => Query().min;
/// <summary>Gets the maximum timer resolution</summary>
public static TimeSpan MaxResolution => Query().max;
/// <summary>Gets/sets the current timer resolution</summary>
public static TimeSpan CurrentResolution
{
get { return Query().cur; }
set
{
var valueInSeconds = value.TotalMilliseconds / 1000.0;
var valueInNanoseconds = valueInSeconds * 1000000000.0;
var valueIn100Nanoseconds = (int)(valueInNanoseconds / 100.0);
NtSetTimerResolution(DesiredResolution: valueIn100Nanoseconds, SetResolution: true, out _);
}
}
}
A little test app on my VM produced these results…
Minimum resolution: 15.6ms Maximum resolution: 0.5ms Current resolution: 15.6ms Attempt to change to 2ms Current resolution: 00:00:00.0020000 DateTime granularity: 00:00:00.0020970 Sleep 0: 00:00:00.0000009 Sleep 1: 00:00:00.0020053 Attempt to change to 5ms Current resolution: 00:00:00.0050000 DateTime granularity: 00:00:00.0050328 Sleep 0: 00:00:00.0000012 Sleep 1: 00:00:00.0049719 Attempt to change to 0.5ms Current resolution: 00:00:00.0005000 DateTime granularity: 00:00:00.0005471 Sleep 0: 00:00:00.0000008 Sleep 1: 00:00:00.0011774 Attempt to change to 15.6ms Current resolution: 00:00:00.0156250 DateTime granularity: 00:00:00.0156280 Sleep 0: 00:00:00.0000011 Sleep 1: 00:00:00.0155707
Short story: writing a unit test for an image processing function, I had the following key parameters for each test:
enum Algorithm { A, B, C };
enum ImageFormat { Gray, Color };
enum ImageSize { Small, Medium, Large };
I wrote a core test function that worked on just one combination of the 3 parameters. E.g.
void Test(
Algorithm algorithm,
ImageFormat imageFormat,
ImageSize imageSize)
{
Console.WriteLine($"Testing algorithm {algorithm} for " +
{imageFormat} image with {imageSize} size");
// the test...
}
Next, I wrote a utility to make iterating the values of an enumeration a little easier.. still not sure why this isn’t part of .Net yet:
class EnumHelper<T>
{
static public T[] Values
{
get { return (T[])Enum.GetValues(typeof(T)); }
}
}
Then, I wrote the nested loops that built each combination and sent them for testing:
void TestAllV1()
{
foreach (var algorithm in EnumHelper<Algorithm>.Values)
{
foreach (var imageFormat in EnumHelper<ImageFormat>.Values)
{
foreach (var imageSize in EnumHelper<ImageSize>.Values)
{
Test(algorithm, imageFormat, imageSize);
}
}
}
}
Now there’s nothing really wrong with the above, but it looked like something that should be able to be written more simply. So I came up with this:
void TestAllV2()
{
var tests =
from algorithm in EnumHelper<Algorithm>.Values
from imageFormat in EnumHelper<ImageFormat>.Values
from imageSize in EnumHelper<ImageSize>.Values
select (algorithm, imageFormat, imageSize);
foreach (var test in tests)
{
Test(test.algorithm, test.imageFormat, test.imageSize);
}
}
The use of the from clause seems better, mainly due to the reduced level of nesting. The Visual Studio 2019 code analysis metrics are interesting:
| Member | MI | CycC | ClsC |
| TestAllV1() | 76 | 4 | 7 |
| TestAllV2() | 69 | 2 | 18 |
Where:
So the foreach approach is (allegedly!) more maintainable, while the from clause method has a lower cyclomatic complexity. This latter metric reinforces the idea that this is slightly simpler than the foreach technique.
It’s also quite easy to add specific filtering inside the tests generator. For example, to quickly stop testing the B algorithm:
var tests =
from algorithm in EnumHelper<Algorithm>.Values
where algorithm != Algorithm.B
from imageFormat in EnumHelper<ImageFormat>.Values
from imageSize in EnumHelper<ImageSize>.Values
select (algorithm, imageFormat, imageSize);
Food for thought 🙂
Edit: actually found another way to do this using the Linq SelectMany method, but I’m not keen on this:
void TestAllV3()
{
var tests =
EnumHelper<Algorithm>.Values.SelectMany(
algorithm => EnumHelper<ImageFormat>.Values.SelectMany(
imageFormat => EnumHelper<ImageSize>.Values.Select(
imageSize => (algorithm, imageFormat, imageSize))));
foreach(var test in tests)
{
Test(test.algorithm, test.imageFormat, test.imageSize);
}
}
