Brew Install Python 2

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  1. Brew Install Python 2.7
  2. Brew Install Python 2 And 3
  3. Brew Install Python 2.7

Warning: This is an old version. The latest stable version is Version 2.0.x.

Python Version¶

So, brew prune (or brew cleanup -prune in newer versions of Homebrew) worked perfectly. It removed all of the above symlinks. Reinstall python and python3 via homebrew. At no time did I touch the python installation located within the /System folder. Oh, and to be clear. The answer to the original question is. Python: Python 2.7.X or 3.4+. After installation, add the Python installation directory and its Scripts subdirectory to your PATH. Depending on your Python version, the defaults would be C: Python27 and C: Python27 Scripts respectively. Npcap: the latest version. Default values are recommended. Scapy will also work with Winpcap.

We recommend using the latest version of Python 3. Flask supports Python 3.5and newer, Python 2.7, and PyPy.

Dependencies¶

These distributions will be installed automatically when installing Flask.

  • Werkzeug implements WSGI, the standard Python interface betweenapplications and servers.

  • Jinja is a template language that renders the pages your applicationserves.

  • MarkupSafe comes with Jinja. It escapes untrusted input when renderingtemplates to avoid injection attacks.

  • ItsDangerous securely signs data to ensure its integrity. This is usedto protect Flask’s session cookie.

  • Click is a framework for writing command line applications. It providesthe flask command and allows adding custom management commands.

Optional dependencies¶

These distributions will not be installed automatically. Flask will detect anduse them if you install them.

  • Blinker provides support for Signals.

  • SimpleJSON is a fast JSON implementation that is compatible withPython’s json module. It is preferred for JSON operations if it isinstalled.

  • python-dotenv enables support for Environment Variables From dotenv when running flaskcommands.

  • Watchdog provides a faster, more efficient reloader for the developmentserver.

Virtual environments¶

Use a virtual environment to manage the dependencies for your project, both indevelopment and in production.

What problem does a virtual environment solve? The more Python projects youhave, the more likely it is that you need to work with different versions ofPython libraries, or even Python itself. Newer versions of libraries for oneproject can break compatibility in another project.

Virtual environments are independent groups of Python libraries, one for eachproject. Packages installed for one project will not affect other projects orthe operating system’s packages.

Python 3 comes bundled with the venv module to create virtualenvironments. If you’re using a modern version of Python, you can continue onto the next section.

If you’re using Python 2, see Install virtualenv first.

Create an environment¶

Create a project folder and a venv folder within:

On Windows:

If you needed to install virtualenv because you are using Python 2, usethe following command instead:

On Windows:

Activate the environment¶

Before you work on your project, activate the corresponding environment:

On Windows:

Your shell prompt will change to show the name of the activated environment.

Install Flask¶

Within the activated environment, use the following command to install Flask:

Flask is now installed. Check out the Quickstart or go to theDocumentation Overview.

Living on the edge¶

If you want to work with the latest Flask code before it’s released, install orupdate the code from the master branch:

Install virtualenv¶

If you are using Python 2, the venv module is not available. Instead,install virtualenv.

On Linux, virtualenv is provided by your package manager:

If you are on Mac OS X or Windows, download get-pip.py, then:

On Windows, as an administrator:

Now you can return above and Create an environment.

  • Warnings
  • Installation
  • PATH and .bash_profile
  • Homebrew - pyenv
  • Uninstall python
    • Homebrew

It’s easy to install multiple versions of python on a Mac computer using installers from python.org, Homebrew, Conda, or other sources. This could create conflicts if a user wants to run one version of python but bash calls a different version instead.

This is guide will show you how to:

  • modify your bash profile to change which version of python is called by bash first.
  • use virtual environments to specify a version of python that will run a project.
  • uninstall specific versions of python.

Mac OS needs python

DO NOT remove any versions of Python found in the following folders:

  • /usr/bin
  • system/Library

These versions of Python—which should be Python 2.7—are installed by Apple and used by Mac OS and other software to perform some functions. Deleting Python from these directories will break Mac OS and force you to reinstall it on your computer.

Other projects may need specific versions of python

You may have a python project or you may use python packages that require particular versions of Python. Uninstalling those versions would prevent those projects or packages from working until that version of python is reinstalled. For example, Python 3 is a dependency of Numpy; if you uninstalled Python 3, then Numpy wouldn’t work until you reinstalled Python 3.

Three common methods of installing python can be found here:

python.org

The python.org (python.org) installer can be found here.


Homebrew

First install Homebrew. The instructions are here, or enter the following command:


To install Python 3:

To install Python 2:


Anaconda

Anaconda is generally used for scientific and machine learning applications.

For Ananconda follow installation instructions here.


Miniconda is a stripped down version of Anaconda.

For Miniconda follow installation instructions here.


PATH

The path is a list of directories that your shell will look through when you execute a command. You can display the path on your computer using the echo $PATH command:

The directories above are separated by a colon, this is what they look like displayed in sequence:

  • /Library/Frameworks/Python.framework/Versions/3.7/bin
  • /Users/username/anaconda3/bin
  • /Library/Frameworks/Python.framework/Versions/2.7/bin
  • /Users/username/miniconda2/bin
  • /Users/username/miniconda3/bin
  • /Library/Frameworks/Python.framework/Versions/3.6/bin
  • /usr/local/bin
  • /usr/bin
  • /bin
  • /usr/sbin
  • /sbin
  • /usr/texbin
  • /opt/X11/bin
  • /usr/X11/bin
  • /usr/local/git/bin

When you ask your shell to run a particular command or run an interpreter, python for example, the shell looks through the different directories listed in the PATH in order they’re presented above. When the shell finds that command, it stops and calls it even if there is another version of the same command, with the same name, further down in the list.

.bash_profile

The bash profile is a set of instructions that are run by the shell when the user logs in to bash. You can add a variety of preferences to the bash profile, including modifications to the PATH. When anaconda, miniconda or other versions of python are installed they automatically add paths to their respective versions of python to the top of the bash profile.

Bash reads the bash profile in sequential order — from top to bottom — and adds those paths to the PATH in the order that they’re read. This means that the last path at the bottom of the bash profile will end up as the first path in the PATH. This means that if you have Python 3.6 installed on your computer, and then decide to add python 3.7, but keep 3.6, the installer will add Python 3.7 to the top of the bash profile but it will end up after python 3.6 in the PATH. Entering python3 in bash will call python 3.6, not 3.7.

If that was confusing compare the order that the python paths are added to my bash profile below to the PATH listed above. You’ll notice that their respective orders are opposite from each other.

Enter the following command to open the bash profile in TextEdit:

Brew Install Python 2.7

My .bash_profile currently looks like this:

If you want to keep all of your installed versions of python, but want bash to open a different version first, just copy and paste it to the bottom of the bash profile. If you don’t want bash to run a particular version of python then delete it from bash profile and uninstall that version by following the instructions further down.

Don’t forget to save the bash profile before closing TextEdit. You also have to reload the bash profile in bash before any changes take effect. Just enter one of the following commands:

  • source ~/.bash_profile
  • . ~/.bash_profile

Pyenv is a Homebrew package that allows a user to install multiple versions of python in Homebrew and specify which version of python they’d like to run.

Install pyenv:

Install different versions of python:

Show which versions of python are installed:

The asterisk indicates that the system version of python is active, but 3.5.0 and 3.6.0 are also installed.


Pyenv Local

Create a folder called PythonLocalProject, then display the version of python called by bash by entering python -V:

Now enter:

This creates a .python-version file which tells pyenv which version of python to run in that directory.

Entering ls -la shows us that file:

Now enter pyenv versions:

And running this command shows which version of python is called by pyenv:

Install python 3.7.1

To change pyenv to the system version of version 3.6.0 enter:

This procedure is fine, you can set a version of python to run in a particular folder. But what if you want to use pyenv to set a global version of python.


Pyenv Global

Pyenv gives these instructions when you enter pyenv init in bash:


Open the bash profile:

  • open ~/.bash_profile

Add this text to the bottom of the file:

  • eval '$(pyenv init -)'

Save the file and then enter:

  • source ~/.bash_profile


Entering echo $PATH will show that a pyenv shim has been added to the beginnning of the path:

  • /Users/username/.pyenv/shims:

And which python will return:

  • /Users/username/.pyenv/shims/python

This means that bash will run the version of python set by pyenv.


Navigate to a folder that doesn’t have a .python-version file and enter:

This shows us that the global version of python is 3.6.0 and it is set by pyenv.

So this shows that bash will run whichever version of python that is set in pyenv.

Brew install python 2.7.17


If you navigate back to the PythonLocalProject folder with the .python-version file and run python -V you will notice that it doesn’t run the global version of python, it runs whichever version was last set with the pyenv local command.



We can use the which command to identify where specific versions of python are located:

This shows some overlap as some versions of python appear in both searches.

The locations of the anaconda and miniconda versions of python are self explanatory, so are the pyenv installs, the python.org installer places python in the /Library/Frameworks/Python.framework/ directory. Homebrew installs all packages, including python, in /usr/local/Cellar, then Homebrew adds a symlink to /usr/local/binso that its version of python can be found in the path. Finally, Apple installs python in /usr/bin. Remember, don’t delete that version.

Follow these instructions if you want to remove particular versions of python.

python.org

The python.org installer places all it’s installed files in the following folders:

  • The system applications folder, /Applications
  • /Library/Frameworks/Python.framework
  • /usr/local/bin

To delete all versions of python that were installed using the python.org installer, enter these commands in terminal:

To remove particular versions of python, you have to refer to the particular framework. The frameworks are installed in /Library/Frameworks/Python.framework and particular versions are found in /Library/Frameworks/Python.framework/Versions/X.Y. So for example if you wanted to uninstall only version 3.5 but leave other versions you would enter the following commands in bash:


Homebrew

To uninstall python that was installed using homebrew you need to identify what versions of python have been installed by Homebrew:

Enter:

Currently brew refers to python3 as python and python 2 is called [email protected].

To uninstall both python2 and python3 enter the following:

Homebrew will refuse to uninstall python if it has dependencies, just uninstall python and ignore the dependencies:

Or, add the dependencies to the list of items to be uninstalled:


Troubleshooting

Brew Install Python 2 And 3

It’s possible to have Homebrew’s Python directory at the beginning of the $PATH but calling python will still start the Apple installed version of Python or some other version. If that’s the case it’s possible that Homebrew’s Python install has become unlinked. This command will unlink and relink Python in Homebrew:

Uninstall Python from Pyenv

To list versions of python installed using pyenv enter:

To uninstall versions of python installed using pyenv enter:

Anaconda

The official removal instructions are found here, but deleting anaconda and miniconda is easy.

Anaconda and miniconda are installed in the users home directory: ~/miniconda2, ~/miniconda3,~/anaconda2, or ~/anaconda3

Depending on which version or versions you have, just enter the following commands:

Anaconda and miniconda also use several invisible files. Delete them by entering this command:


  • Python Removal Instructions - towards the bottom of the README file.

And now for something completely different.

Brew Install Python 2.7