MacOS comes by default with Python 2.7 which, at this point, receives only bug fixes and will be EOL by 2020. Python 3.x is the future and it is supported by all major Python libraries. In this tutorial, we’ll use the Python 3.8. Start by installing the Command Line Tools for macOS. Question or issue on macOS: I am developping a simple Python application using a PySide2 GUI. It currently works fine in Windows, Linux and Mac. On Windows, I could use PyInstaller and InnoSetup to build a simple installer. Then I tried to do the same thing on Mac. It soon broke, because the system refused. I am experiencing a Python menu issue on both of my Mac's. One Mac has macOS Catalina and Python 3.7.4 via pyEnv with Tcl/Tk 8.6.9 and the other has macOS Catalina and Python 3.8.0. Via pyEnv and Tcl/Tk 8.6.9 and both area exhibiting the same behavior. This behavior did not exist before upgrading from macOS Mojave to macOS Catalina. Think to remove this version and reinstall. Read this post, How to uninstall Python 2.7 on a Mac OS X 10.6.4? One post reminds not to remove Mac built in python. I have multiple versions of python managed by pyenv. Just wonder where could I check Mac Catalina 10.15 built in python version?

Posted on October 21, 2019 by Paul

Updated 11 February 2020

Python itself does not provide a macOS GUI application interface; that is something that IDLE does (and other third-party IDEs that support Python). The Launcher app dates back to the very earliest days of Mac OS X when Python for Classic MacOS (System 9) was ported over.

In this article, I will show you how to install OpenCV 4 with Python 3 on macOS Catalina.

There is also a video version of this tutorial:

MacOS comes by default with Python 2.7 which, at this point, receives only bug fixes and will be EOL by 2020. Python 3.x is the future and it is supported by all major Python libraries. In this tutorial, we’ll use the Python 3.8.

Start by installing the Command Line Tools for macOS. Please note, that you will need the Command Line Tools even if you’ve already installed Xcode. Open a Terminal and write:

Once the Command Line Tools are installed, we can install Python.

The official installer of Python is a pkg file that will start a GUI installer which will guide you through the installation. You can also check the video version of this tutorial if you want to see how I did it.

As a side note, you can have multiple Python 3 versions installed on your macOS machine. If this is the case, you can select which version you want to use by specifying the version number, e.g.:

or:

After the above, you can invoke Python 3.8 using the python3.8 command. python3 will also invoke the latest installer version of Python 3. This is what I see if I run python3.8 on my machine:

Next, let’s follow best practices and create a new Python environment in which we can install NumPy and OpenCV:

At this point, your prompt should indicate that you are using the work environment. You can read more about Python environments in the documentation.

Once an environment is activated, all the install commands will apply only to the current environment. By default, if you close your Terminal, the environment is deactivated. If you want to be able to use it, use the source work/bin/activate command.

We can install NumPy and OpenCV with:

Please note that the above will install the slightly older OpenCV 4.1, latest binary version doesn’t seem to work on macOS Catalina!

As a side note, when you are in a new environment you can use python to invoke the Python interpreter, no need to use the version number.

At this point, you should have OpenCV 4 and Python installed on your Mac. We can write a small test program that will print the OpenCV version, load an image from the disk, convert the image to gray and show the result. Start by downloading the next image:

Save it as clouds.jpg. In the same folder where you’ve saved the above image, create a new file demo.py and write the next code:

Run the code with:

(You can close the two windows by pressing ESC!)

You should see something like in the next figure. By default, the last image (the gray one) will be over the first one. You need to move the window in order to see both images:

If you want to learn more about OpenCV and Python I would recommend reading OpenCV with Python Blueprints by M. Beyeler:

or, OpenCV with Python By Example by G. Garrido and P. Joshi:

Bob Savage <bobsavage@mac.com>

Python on a Macintosh running Mac OS X is in principle very similar to Python onany other Unix platform, but there are a number of additional features such asthe IDE and the Package Manager that are worth pointing out.

4.1. Getting and Installing MacPython¶

Mac OS X 10.8 comes with Python 2.7 pre-installed by Apple. If you wish, youare invited to install the most recent version of Python 3 from the Pythonwebsite (https://www.python.org). A current “universal binary” build of Python,which runs natively on the Mac’s new Intel and legacy PPC CPU’s, is availablethere.

What you get after installing is a number of things:

• A Python3.9 folder in your Applications folder. In hereyou find IDLE, the development environment that is a standard part of officialPython distributions; and PythonLauncher, which handles double-clicking Pythonscripts from the Finder.

• A framework /Library/Frameworks/Python.framework, which includes thePython executable and libraries. The installer adds this location to your shellpath. To uninstall MacPython, you can simply remove these three things. Asymlink to the Python executable is placed in /usr/local/bin/.

The Apple-provided build of Python is installed in/System/Library/Frameworks/Python.framework and /usr/bin/python,respectively. You should never modify or delete these, as they areApple-controlled and are used by Apple- or third-party software. Remember thatif you choose to install a newer Python version from python.org, you will havetwo different but functional Python installations on your computer, so it willbe important that your paths and usages are consistent with what you want to do.

IDLE includes a help menu that allows you to access Python documentation. If youare completely new to Python you should start reading the tutorial introductionin that document.

If you are familiar with Python on other Unix platforms you should read thesection on running Python scripts from the Unix shell.

4.1.1. How to run a Python script¶

Your best way to get started with Python on Mac OS X is through the IDLEintegrated development environment, see section The IDE and use the Help menuwhen the IDE is running.

If you want to run Python scripts from the Terminal window command line or fromthe Finder you first need an editor to create your script. Mac OS X comes with anumber of standard Unix command line editors, vim andemacs among them. If you want a more Mac-like editor,BBEdit or TextWrangler from Bare Bones Software (seehttp://www.barebones.com/products/bbedit/index.html) are good choices, as isTextMate (see https://macromates.com/). Other editors includeGvim (http://macvim-dev.github.io/macvim/) and Aquamacs(http://aquamacs.org/).

To run your script from the Terminal window you must make sure that/usr/local/bin is in your shell search path.

To run your script from the Finder you have two options:

• Drag it to PythonLauncher

• Select PythonLauncher as the default application to open yourscript (or any .py script) through the finder Info window and double-click it.PythonLauncher has various preferences to control how your script islaunched. Option-dragging allows you to change these for one invocation, or useits Preferences menu to change things globally.

4.1.2. Running scripts with a GUI¶

With older versions of Python, there is one Mac OS X quirk that you need to beaware of: programs that talk to the Aqua window manager (in other words,anything that has a GUI) need to be run in a special way. Use pythonwinstead of python to start such scripts.

Python Os X Catalina

With Python 3.9, you can use either python or pythonw.

4.1.3. Configuration¶

Python on OS X honors all standard Unix environment variables such asPYTHONPATH, but setting these variables for programs started from theFinder is non-standard as the Finder does not read your .profile or.cshrc at startup. You need to create a file~/.MacOSX/environment.plist. See Apple’s Technical Document QA1067 fordetails.

For more information on installation Python packages in MacPython, see sectionInstalling Additional Python Packages.

4.2. The IDE¶

MacPython ships with the standard IDLE development environment. A goodintroduction to using IDLE can be found athttp://www.hashcollision.org/hkn/python/idle_intro/index.html.

4.3. Installing Additional Python Packages¶

There are several methods to install additional Python packages:

• Packages can be installed via the standard Python distutils mode (pythonsetup.pyinstall).

• Many packages can also be installed via the setuptools extensionor pip wrapper, see https://pip.pypa.io/.

4.4. GUI Programming on the Mac¶

There are several options for building GUI applications on the Mac with Python.

Python Version Macos Catalina

PyObjC is a Python binding to Apple’s Objective-C/Cocoa framework, which isthe foundation of most modern Mac development. Information on PyObjC isavailable from https://pypi.org/project/pyobjc/.

The standard Python GUI toolkit is tkinter, based on the cross-platformTk toolkit (https://www.tcl.tk). An Aqua-native version of Tk is bundled with OSX by Apple, and the latest version can be downloaded and installed fromhttps://www.activestate.com; it can also be built from source.

wxPython is another popular cross-platform GUI toolkit that runs natively onMac OS X. Packages and documentation are available from https://www.wxpython.org.

PyQt is another popular cross-platform GUI toolkit that runs natively on MacOS X. More information can be found athttps://riverbankcomputing.com/software/pyqt/intro.

4.5. Distributing Python Applications on the Mac¶

The standard tool for deploying standalone Python applications on the Mac ispy2app. More information on installing and using py2app can be foundat http://undefined.org/python/#py2app.

4.6. Other Resources¶

The MacPython mailing list is an excellent support resource for Python users anddevelopers on the Mac:

Python For Mac Catalina

Another useful resource is the MacPython wiki: