1) Introduction
Paste script is a part of Python Paste web development utilities.
Its paster create command is used by various Python frameworks to generate skeleton code for a development project.
2) Paster and local commands
Besides generic project templates, paster provides local commands which are project aware commands to add more modules into an existing project. Local commands are made available by paster extensions. For example, ZopeSkel product has various local commands to generate skeletons into Plone/Zope projects automatically
- Views
- Content types
- Forms
- Portlets
… and so on.
For example, you could generate a project template for Plone add-on module and then create content types there using a local paster command. The local commands become available when you execute paster command in the folder of your project.
Example:
paster create -t archetype myorg.customploneaddon
cd src/myorg.customploneaddon
# Now new paster commands are available
paster
Usage: ../../bin/paster COMMAND
usage: paster [paster_options] COMMAND [command_options]
...
Commands:
...
ZopeSkel local commands:
addcontent Adds plone content types to your project
Above, ZopeSkel paster template adds its addcontent templates. Now you can use addcontent local command to contribute to the existing project
paster addcontent -t contenttype MyShinyWebPage
2.1. ZopeSkel
For more information how to use paster to create add-ons and add-on submodules for Plone, see here.
To see list of available paster local commands, run paster command
../../bin/paster addcontent --list
… in your development project. For ZopeSkel specific projects the output should be something like this:
Available templates:
atschema: A handy AT schema builder
contenttype: A content type skeleton
form: A form skeleton
3) How paster local commands work
paster reads (evaluates) setup.py file which declares a Python egg. If it founds paster_plugins section there, it will look for local commands there. For example, Plone project templates declare the following paste_plugins in setup.py:
paster_plugins = ["ZopeSkel"]
4) setup.py install_requires
Python modules can dependencies to other modules using setup.py and install_requires section. For example, a Plone add-on might read:
install_requires=['setuptools',
# -*- Extra requirements: -*-
"five.grok",
"plone.directives.form"
],
This means that when you use setuptools/buildout/pip/whatever Python package installation tool to install a package from Python Package Index (PyPi) it will also automatically install dependency packages declared in install_requires.
4.1. paster and install_requires
This is where things usually go haywire.
Let’s assume you are using paster in a project which contains N python packages. You probably use an external configuration system to manage your installed applications and their versions to make repeatable deployments possible (hint: buildout is gaining traction in Python community lately).
Paster is not aware of this external Python package configuration set (paster cannot see them in its PYTHONPATH). So what happens when you try to execute paster create which reads setup.py containing install_requires and encounters dependencies?
Paster will try automatically download and install them locally in that folder.
Plone and Zope ecosystem contains over hundreds of reusable components, in nice dependency hierarchy. paster create would try to pull all them in to your source tree as *.egg folders. See discussion here.
Warning
Do not never use system paster command.
Do not ever run sudo easy_install ZopeSkel. Do not ever run paster local commands using a paster command from your system-wide Python installation.
Warning
The internet is full of tutorial saying easy_install ZopeSkel. If you ever encounter this kind of tutorial, it’s wrong.
5) Paste and buildout
If you are using buildout to manage your Python application deployment, you can integrate paster nicely with it.
Add to your buildout.cfg:
parts =
...
paster
[paster]
recipe = zc.recipe.egg
eggs =
PasteScript
ZopeSkel
${instance:eggs}
After rerunning buildout, buildout adds paster command to bin folder.
Then you can run paster from buildout folder:
bin/paster
… or in a buildout managed project under src folder…
../../bin/paster
This way paster is aware of your deployment configuration and local commands won’t explode on your face anymore.
Thanks Martin Aspeli to helping with how buildout + paster should be done.
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