Installed Python 3 On Mac OS X But It Still Use Python 2.7

Mac OS X has installed python by default, but the version is 2.7.10. It is a little older, so I upgrade python to a newer version ( python 3.7 or python 3.9 ). But after installing the new version, when I open a terminal and run python command, it still uses Python 2.7. This article will tell you how to fix it.

1. Install Python 3.7 & Python 3.9.

Go to python download page and click the related link to download.
After download, double click the installer to install it follow the wizard ( you can refer Install Python Linux And MacOS Version Tutorial ).
When the installation process completes successfully. Open a Finder, click Go —> Go to Folder… menu item at the top menu bar.
Input /Library/Frameworks/Python.framework/Versions in above Go to Folder dialog, click Go button.
Now you can see all the 3 python version has been installed in the /Library/Frameworks/Python.framework/Versions folder.

2. How To Fix Installed Python3 But Still Python 2.7 Is Used Error.

Now when you execute the python command in a terminal, you will find it still uses the old version which is 2.7.
```
$ python
Python 2.7.10 (default, Oct6 2017, 22:29:07)
```

To use the new Python version, you need to run python3 in the terminal.

$ python3
Python 3.9.1 (v3.9.1:1e5d33e9b9, Dec 7 2020, 12:10:52) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

To exit the Python interactive interpreter, input command exit(). Then you can go back to the terminal bash environment again.

$ python3
Python 3.9.1 (v3.9.1:1e5d33e9b9, Dec 7 2020, 12:10:52) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

To get the current python version, add uppercase -V as the python command parameter like below.
```
$ python -V
Python 2.7.10

$ python3 -V
Python 3.9.1
```
But how to make python command invokes python 3.7 or python 3.9 instead of python 2.7, you can follow the below steps.
Run echo $PATH command in a terminal, you can see python 3.9 and python 2.7 ‘s bin directory are all at the beginning of the PATH system environment variable.
```
$ echo $PATH
/Library/Frameworks/Python.framework/Versions/3.9/bin:/Library/Frameworks/Python.framework/Versions/2.7/bin:......
```

Go to /Library/Frameworks/Python.framework/Versions/3.9/bin directory, list all the files inside the directory, you can see the command file python3 is linked to another executable file python3.9.

$ cd /Library/Frameworks/Python.framework/Versions/3.9/bin
$ ls -l
total 120
......
lrwxr-xr-x  1 root  admin      9 Jan 23 14:15 python3 -> python3.9
......
-rwxrwxr-x  1 root  admin  29008 Dec  8 01:17 python3.9
......

So you can run the command python3.9 to invoke python 3.9 interactive interpreter.

$ python3.9
Python 3.9.1 (v3.9.1:1e5d33e9b9, Dec  7 2020, 12:10:52) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

If you want to make the python command invoke Python 3.9 by default, you can create a new file python and link it to the python3.9 executable file in /Library/Frameworks/Python.framework/Versions/3.9/bin directory.
```
# Below command create the new python and link it to file python3.9.
$ ln -s python3.9 python

$ ls -l
......
lrwxr-xr-x 1 songzhao admin 9 Jan 24 10:45 python -> python3.9
......
```

Now when you run python in the command line, it will invoke Python 3.9 as default.

$ python
Python 3.9.1 (v3.9.1:1e5d33e9b9, Dec  7 2020, 12:10:52) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

If you want to make Python 3.7 the default Python interactive interpreter, you can add directory /Library/Frameworks/Python.framework/Versions/3.7/bin at the beginning of PATH system environment variable follow below steps.
Run cd ~ to go to your home directory. Run vim .bash_profile to edit it.
```
$ cd ~
$ pwd
/Users/songzhao
$ vim .bash_profile
```

Add below code at the end of the .bash_profile file.

PATH="/Library/Frameworks/Python.framework/Versions/3.7/bin:${PATH}"
export PATH

Press :wq! in vim to save the changes and exit.
Run source .bash_profile command to make it effective.
Run echo $PATH to see the /Library/Frameworks/Python.framework/Versions/3.7/bin path is at the beginning of the PATH value, so the file inside this directory will be invoked first.
```
$ echo $PATH
/Library/Frameworks/Python.framework/Versions/3.7/bin:/Library/Frameworks/Python.framework/Versions/2.7/bin......
```
Now when you run the command python, it will still invoke Python 2.7.
Create a file python and link it to file python3.7 in /Library/Frameworks/Python.framework/Versions/3.7/bin directory.
```
$ ln -s python3.7 python
```
Now run python in command, it will invoke Python 3.7 by default.

3. How To Fix Still Use Old PIP Version Issue After Install Python 3.

Now when you run command pip in a terminal, it still uses the pip command provided by python 2.

$ pip -V
pip 6.1.1 from /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages (python 2.7)

Now we want to make pip command to execute the new pip version which is provided by python 3.
Run command which python to show the current python binary file saved directory.
```
$ which python
/Library/Frameworks/Python.framework/Versions/3.9/bin/python
```

Go to the above folder, you can see there is a pip3 file in the folder.

$ cd /Library/Frameworks/Python.framework/Versions/3.9/bin
$ ls -l
total 136
......
-rwxrwxr-x  1 root      admin    268 Jan 23 14:15 pip3
......

Run command ln pip3 pip to create pip file and link the file to pip3.

$ ln pip3 pip
$ ls -l
......
-rwxrwxr-x  2 root      admin    268 Jan 23 14:15 pip
-rwxrwxr-x  2 root      admin    268 Jan 23 14:15 pip3
......

Open a new terminal, run command pip -V, now you can see it will use the new pip version.

$ pip -V
pip 20.2.3 from /Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/pip (python 3.9)