pip + virtualenv

More WHY? than HOW?

What’s pip?

pip is a tool for installing and managing Python packages.

It’s similar to yum, apt, homebrew, rubygems, etc...

$ easy_install pip

How do you get pip?

easy_install is a tool for installing and managing Python packages.

Wait. What’s easy_install?

But wait; there’s more!If you’re using a *NIX system, you can probably install pip via your OS’s package manager.

You can probably also install Python packages using your OS’s package manager.

So why use pip over X?easy_install:

● I honestly don’t know, but if you enjoy parroting, click here: http:

//www.pip-installer.org/en/latest/other-tools.html#pip-compared-

to-easy-install

Your OS’s package manager:

● Versions are usually outdated, especially for large projects

Basic pip usage...# Searching...

$ pip search json

# Installing...

$ sudo pip install simplejson

# Updating…

$ sudo pip install --upgrade simplejson

# Uninstalling…

$ sudo pip uninstall simplejson

What’s virtualenv?

virtualenv is a tool for creating isolated Python environments.

It’s similar to chroot, FreeBSD jails, Ruby’s bundler, etc...

Why or when do we need virtualenv?

To answer that, we have to ask another question.

A system-wide install!

What happens when you install something with pip?

Why is this bad?● Only one version for the entire

machine.● You’ll end up with a lot of packages on

/usr/local● I totally made the second one up so I

can use bullet points

Main use cases:● Different projects are going to need

different versions of packages.● Provide packages only to the projects

that need them.

TIP!

One virtualenv for each project/repo you’re working on.

Basic virtualenv usage...# Creating a virtualenv...

$ virtualenv ENV # creates a directory named ENV

# Activating a virtualenv

$ source bin/activate

# Manage your virtualenv’s packages

# A new virtualenv includes pip in ENV/bin/pip

...

# Leaving a virtualenv

$ source bin/deactivate

I don’t really use virtualenv.

CONFESSION TIME

Use virtualenvwrapper.

Vanilla virtualenv makes me want to cry.

Basic virtualenvwrapper usage...# Creating a virtualenv...

$ mkvirtualenv env_name

# Activating a virtualenv

$ workon env_name

# Manage your virtualenv’s packages

# (install, update, uninstall, etc)

...

# Leaving a virtualenv

$ deactivate

REMEMBER!

Everything that happens between workon and deactivate only apply to the current virtualenv.

For virtualenvs that you can “pass around”# Save all the packages you are using to a file...

$ pip freeze > requirements.txt

# Install all packages you needed from a file...

$ pip install -r requirements.txt

# Especially useful for projects with more than one person working on it...

Because non sequitur...

BONUS

virtualenvs and environment variables...#!/bin/bash

# $WORKON_HOME/pizzapy/bin/postactivate

export DB_NAME=pizzapy

export DB_USER=root

export DB_PASSWORD=a1f9234a0f2cbd028

export DB_HOST=192.20.12.98

export DB_PORT=3306

virtualenvs and environment variables...# in your Python code...

import os

DATABASES = {

‘default’: {

‘NAME’: os.environ[‘DB_NAME’]

‘USER’: os.environ[‘DB_USER’]

‘PASSWORD’: os.environ[‘DB_NAME’]

‘NAME’: os.environ[‘DB_PASSWORD’]

‘HOST’: os.environ[‘DB_HOST’]

}

}

Questions?

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