Install Pyqt For Python 3 Mac

Many people want to use Qt Designer without having to download gigabytes of other software. Here are small, standalone installers of Qt Designer for Windows and Mac:

If you encounter any problems, please just send us an email. We'd be happy to help.

Feb 08, 2017  Installing PyQt4 On Mac OSX. Posted on February 8, 2017 July 24. Brew install cartr/qt4/pyqt Installing Python. Next, you need to create a clean install of Python 2.7 via Homebrew: brew install python Setting Up The Environment. It probably does install Python 3. That’s not going to cause a problem, as it also installs.

What is Qt Designer?

Qt Designer is a tool for quickly building graphical user interfaces with widgets from the Qt GUI framework. It gives you a simple drag-and-drop interface for laying out components such as buttons, text fields, combo boxes and more. Here is a screenshot of Qt Designer on Windows:

Qt Designer produces .ui files. This is a special XML-based format that stores your widgets as a tree. You can either load these files at runtime, or have them translated to a programming language such as C++ or Python.

Qt Designer and Python

Many people like to use Qt Designer together with Python because it is a dynamic language that lends itself well to rapid prototyping. The easiest way to combine the two is via the PyQt bindings. To install PyQt, simply enter the following on the command line:

(This assumes you have Python 3 installed.)

Suppose you have saved your file from Qt Designer as dialog.ui. Then you can create another file, say main.py, with the following contents:

When you then invoke python3 main.py on the command line, your dialog should open:

(If you have closed the command prompt in the meantime, you may have to execute the source / call statement from above again.)

Qt Designer vs. Qt Creator

Qt Designer normally ships as a part of Qt Creator. This is Qt's official editor / IDE and lets you do a lot more than just graphically design user interfaces. It is a full-fledged and very powerful C++ IDE. This power comes at a price however: The download for Qt Creator is gigabytes in size!

This page was created for people who only need Qt Designer. The download links here contain minimal, self-contained installers of just Qt Designer that are orders of magnitude smaller. Here they are again:

Enjoy!

Michael has been working with Qt and Python since 2016, when he started fman, a cross-platform file manager. Frustrated with the many difficulties of creating a desktop application, Michael open sourced fman's build system (fbs). It lets you create GUIs with Qt and Python in minutes instead of months!

This PyQt5 tutorial shows how to use Python 3 and Qt to create a GUI on Windows, Mac or Linux. It even covers creating an installer for your app.

What is PyQt5?

PyQt is a library that lets you use the Qt GUI framework from Python. Qt itself is written in C++. By using it from Python, you can build applications much more quickly while not sacrificing much of the speed of C++.

PyQt5 refers to the most recent version 5 of Qt. You may still find the occasional mention of (Py)Qt4 on the web, but it is old and no longer supported.

An interesting new competitor to PyQt is Qt for Python. Its API is virtually identical. Unlike PyQt, it is licensed under the LGPL and can thus be used for free in commercial projects. It's backed by the Qt company, and thus likely the future. We use PyQt here because it is more mature. Since the APIs are so similar, you can easily switch your apps to Qt for Python later.

Install PyQt

The best way to manage dependencies in Python is via a virtual environment. A virtual environment is simply a local directory that contains the libraries for a specific project. This is unlike a system-wide installation of those libraries, which would affect all of your other projects as well.

To create a virtual environment in the current directory, execute the following command:

This creates the venv/ folder. To activate the virtual environment on Windows, run:

On Mac and Linux, use:

You can see that the virtual environment is active by the (venv) prefix in your shell:

To now install PyQt, issue the following command:

The reason why we're using version 5.9.2 is that not all (Py)Qt releases are equally stable. This version is guaranteed to work. Besides this subtlety – Congratulations! You've successfully set up PyQt5.

Create a GUI

Time to write our very first GUI app! With the virtual environment still active, start Python. We will execute the following commands:

First, we tell Python to load PyQt via the import statement:

Next, we create a QApplication with the command:

This is a requirement of Qt: Every GUI app must have exactly one instance of QApplication. Many parts of Qt don't work until you have executed the above line. You will therefore need it in virtually every (Py)Qt app you write.

The brackets [] in the above line represent the command line arguments passed to the application. Because our app doesn't use any parameters, we leave the brackets empty.

Now, to actually see something, we create a simple label:

Then, we tell Qt to show the label on the screen:

Depending on your operating system, this already opens a tiny little window:

The last step is to hand control over to Qt and ask it to 'run the application until the user closes it'. This is done via the command:

If all this worked as expected then well done! You've just built your first GUI app with Python and Qt.

Widgets

Everything you see in a (Py)Qt app is a widget: Buttons, labels, windows, dialogs, progress bars etc. Like HTML elements, widgets are often nested. For example, a window can contain a button, which in turn contains a label.

The following screenshot shows the most common Qt widgets:

Top-to-bottom, left-to-right, they are:

You can download the code for the app shown in the screenshot here, if you are interested.

Layouts

Like the example above, your GUI will most likely consist of multiple widgets. In this case, you need to tell Qt how to position them. For instance, you can use QVBoxLayout to stack widgets vertically:

The code for this screenshot is:

As before, we instantiate a QApplication. Then, we create a window. We use the most basic type QWidget for it because it merely acts as a container and we don't want it to have any special behavior. Next, we create the layout and add two QPushButtons to it. Finally, we tell the window to use this layout (and thus its contents). As in our first application, we end with calls to .show() and app.exec_().

There are of course many other kinds of layouts (eg. QHBoxLayout to lay out items in a row). See Qt's documentation for an overview.

Custom styles

One of Qt's strengths is its support for custom styles. There are many mechanisms that let you customize the look and feel of your application. This section outlines a few.

Built-in styles

The coarsest way to change the appearance of your application is to set the global Style. Recall the widgets screenshot above:

This uses a style called Fusion. If you use the Windows style instead, then it looks as follows:

To apply a style, use app.setStyle(..):

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The available styles depend on your platform but are usually 'Fusion', 'Windows', 'WindowsVista' (Windows only) and 'Macintosh' (Mac only).

Custom colors

If you like a style, but want to change its colors (eg. to a dark theme), then you can use QPalette and app.setPalette(..). For example:

This changes the text color in buttons to red:

For a dark theme of the Fusion style, see here.

Style sheets

In addition to the above, you can change the appearance of your application via style sheets. This is Qt's analogue of CSS. We can use this for example to add some spacing:

For more information about style sheets, please see Qt's documentation.

Signals / slots

Qt uses a mechanism called signals to let you react to events such as the user clicking a button. The following example illustrates this. It contains a button that, when clicked, shows a message box:

The interesting line is highlighted above: button.clicked is a signal, .connect(..) lets us install a so-called slot on it. This is simply a function that gets called when the signal occurs. In the above example, our slot shows a message box.

The term slot is important when using Qt from C++, because slots must be declared in a special way in C++. In Python however, any function can be a slot – we saw this above. For this reason, the distinction between slots and 'normal' functions has little relevance for us.

Signals are ubiquitous in Qt. And of course, you can also define your own. This however is beyond the scope of this tutorial.

Compile your app

You now have the basic knowledge for creating a GUI that responds to user input. Say you've written an app. It runs on your computer. How do you give it to other people, so they can run it as well?

You could ask the users of your app to install Python and PyQt like we did above, then give them your source code. But that is very tedious (and usually impractical). What we want instead is a standalone version of your app. That is, a binary executable that other people can run on their systems without having to install anything.

In the Python world, the process of turning source code into a self-contained executable is called freezing. Although there are many libraries that address this issue – such as PyInstaller, py2exe, cx_Freeze, bbfreze, py2app, .. – freezing PyQt apps has traditionally been a surprisingly hard problem.

We will use a new library called fbs that lets you create standalone executables for PyQt apps. To install it, enter the command:

Then, execute the following:

This prompts you for a few values:

When you type in the suggested run command, an empty window should open:

This is a PyQt5 app just like the ones we have seen before. Its source code is in src/main/python/main.py in your current directory. But here's the cool part: We can use fbs to turn it into a standalone executable!

This places a self-contained binary in the target/MyApp/ folder of your current directory. You can send it to your friends (with the same OS as yours) and they will be able to run your app!

(Please note that fbs currently targets Python 3.5 or 3.6. If you have a different version and the above does not work, please install Python 3.6 and try again. On macOS, you can also install Python 3.5 with Homebrew.)

Bonus: Create an installer

fbs also lets you create an installer for your app via the command fbs installer:

(If you are on Windows, you first need to install NSIS and place it on your PATH.)

For more information on how you can use fbs for your existing application, please see this article. Or fbs's tutorial.

Summary

If you have made it this far, then big congratulations. Hopefully, you now have a good idea of how PyQt (and its various parts) can be used to write a desktop application with Python. We also saw how fbs lets you create standalone executables and installers.

Due to the popularity of this article, I wrote a book about PyQt5. It's a great next resource for creating your own apps, if you want to learn more. Have fun!

Michael has been working with PyQt5 since 2016, when he started fman, a cross-platform file manager. Frustrated with the many challenges of creating a desktop application, Michael open sourced fman's build system (fbs). It lets you create PyQt GUIs in in minutes instead of months!