If you are a pip¹ and virtualenv user you already know how easy it is to install python packages. Unlike the bad old days when I started programming in Python, 9 years ago, it is now easy to add, remove and manage python modules. In fact we can leverage pip to create an update command for a python program, for example and ease of illustration, a shell utility.

Table of Contents

1. Desired Features
2. Basic Idea
3. Implementation

Desired Features

• Uses a server controlled by the owner (instead of the Python Package Index).
• Install an arbitrary version of the program.
• Defaults to updating to the newest version of the major release one is tracking.

I often want my programs to update themselves from a specific location. For instance an internal server or perhaps my github account. Fortunately pip already supports such nicities with the -e for the install command.

Additionally, when running a generic update you often want to stay on the same major revision and simply get the bug fixes. However, it is important to provide the option to update to any arbitrary release including tracking the master branch.

Basic Idea

Use Pip and the -e option plus a base URL to automatically update your software. eg. Have you software run pip for the user.

example command:

pip install --upgrade --src="$HOME/.src" -e git+<URL>@<REV>#egg=PACKAGE_NAME

Tracking Major Versions

To track major version updates some care must be taken in setting up the repository. I use branches instead of tags to track major releases. This allows me to push out bug fix updates for every one tracking that release. I tag minor releases to allow users to install a specific version.

Branches

• master
• stable
• r0.1
• r0.2
• ...
• rN

Tags

• r0.1
• r0.1.1
• r0.1.x
• ...
• rN

Pip Gotcha

When checking out branches using pip you have to supply origin/branchname ex:

pip install --upgrade --src="$HOME/.src" -e git+https://github.com/user/repo.git@origin/branch#egg=PACKAGE_NAME

While when checking out a commit you should not supply origin

pip install --upgrade --src="$HOME/.src" -e git+https://github.com/user/repo.git@COMMIT_ID#egg=PACKAGE_NAME

Why does pip work like this? Because of the commands it executes. For the command:

pip install --upgrade --src="$HOME/.src" -e git+https://github.com/user/repo.git@<VERSION>#egg=PACKAGE_NAME

pip runs

git fetch -q git reset --hard -q <VERSION>

Store the tracked version in the source

To ensure the update command installs the correct updates I put which release to checkout in the source code. This allows me to "release" a version by creating a branch and then changing the RELEASE constant to point the name of the branch.

Implementation

Note: This is example code only, you should modify for security and stability of your enviroment.

Note: I didn't include virtualenv support in this code but it is trivial to add.

from subprocess import check_call as run 
from getopt import getopt, GetoptError 
RELEASE = 'master' # default release 
SRC_DIR = "$HOME/.src" # checkout directory 
UPDATE_CMD = ( # base command 
'pip install --src="%s" --upgrade -e ' 
'git://github.com/timtadh/swork.git@%s#egg=swork' 
)

@command 
def update(args): 
    try: 
        opts, args = getopt(args, 'sr:', ['sudo', 'src=', 'release=', 'commit=']) 
    except GetoptError, err: 
        log(err) 
        usage(error_codes['option'])

    sudo = False 
    src_dir = SRC_DIR 
    release = RELEASE 
    commit = None 
    for opt, arg in opts: 
        if opt in ('-s', '--sudo'): 
            sudo = True 
        elif opt in ('-r', '--release'): 
            release = arg 
        elif opt in ('--src',): 
            src_dir = arg 
        elif opt in ('--commit',): 
            commit = arg

    if release[0].isdigit(): ## Check if it is a version 
        release = 'r' + release 
    release = 'origin/' + release ## assume it is a branch

    if commit is not None: ## if a commit is supplied use that 
        cmd = UPDATE_CMD % (src_dir, commit) 
    else: 
        cmd = UPDATE_CMD % (src_dir, release)

    if sudo: 
        run('sudo %s' % cmd) 
    else: 
        run(cmd)