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Use python to write configuration in zc.buildout

Project description


travis pyversions

A quick way to build recipes by using python directly inside zc.buildout

Supported options

The recipe supports any number of options, which are Python functions. Since the ini parser used with buildout doesn’t preserve initial whitespace each line of your method should start with a followed by the whitespace as per normal python. They will look like this:

recipe = mr.scripty
MAX = 10
function1 =
  ... x = range(1,int(self.MAX))
  ... return ' '.join(x)

recipe = something.recipe
argument = ${myscripts:function1}

The return value will be stored as a value in the buildout parts options which is available for replacement in other buildout parts. What is returned is always converted to a string.

Functions vs Constants

Options all in upper case are treated as string constants and added to the Recipe instance as an attribute. All other options will be treated as python functions.

As each option is a Python function or variable, it needs to possess an acceptable function identifier (see For instance, typical buildout options with hyphens (such as environment-vars) will be invalid.

Since these functions are actually methods self is an available local variable which refers to the recipe instance. self.options, self.buildout and are available.

Any option beginning with _ is not evaluated so can be used as a private function.

Init, Install and Update

There are three special functions which are evaluated regardless if they are called from another recipe and whose value isn’t stored.

init: Init is called everytime the recipe is loaded. This function allows you to reduce the need for multiple functions that may do similar jobs, remove the need for a dummy option in order to execute arbitrary code (and other uses), like so:

recipe = mr.scripty
init =
    ... import math
    ... self.options['pi'] = str(math.pi)
    ... self.options['e'] = str(math.e)
    ... self.options['sqrt_two'] = str(math.sqrt(2))

After running buildout, the options pi, e, and sqrt_two will all be available for use against the myscripts section like so: ${myscripts:sqrt_two}. See the example regarding Offsetting port numbers for more information.

install is called if the arguments (functions or constants) have changed since the last run or if it’s never run before.

update is called each time (but after init)

These can be used as quick in-place replacement for creating a real recipe and have the same semantics as detailed in

Bugs and Repo


Tranforming Varnish backends for HAProxy

Let’s say you want to transform a varnish:backends value to what can be used inside haproxy:

>>> write('buildout.cfg',
... """
... [buildout]
... parts = scripty echobackends echorepeat
... [varnish]
... backends =
... [scripty]
... recipe = mr.scripty
... backends =
...   ... res = ""
...   ... for line in self.buildout['varnish']['backends'].splitlines():
...   ...    if ':' not in line:
...   ...      continue
...   ...    host, dest = line.strip().split(':')
...   ...    host = host.split('.')[0]
...   ...    res += "acl {} url_sub VirtualHostRoot/{}\\n".format(host, dest)
...   ... return res
... repeat =
...   ... opt_repeatx = int('10')
...   ... fun_repeatx = self.repeatx()
...   ... return '\\n'.join(["this is line %s"%i for i in range(1,opt_repeatx+1)])
... repeatx = return '10'
... [echobackends]
... recipe = mr.scripty
... install = print(self.buildout['scripty']['backends']); return []
... [echorepeat]
... recipe = mr.scripty
... install =
...   ... script = self.buildout['scripty']
...   ... print(script['repeat'])
...   ... return []
... """)

Running the buildout gives us:

>>> print(system(buildout))
Installing scripty.
Installing echobackends.
acl myhost url_sub VirtualHostRoot/
acl myhost2 url_sub VirtualHostRoot/
Installing echorepeat.
this is line 1
this is line 2
this is line 3
this is line 4
this is line 5
this is line 6
this is line 7
this is line 8
this is line 9
this is line 10...

From this example you’ll notice several things. Options that are part of a mr.scripty part are turned into methods of the part instance and can call each other. In addition, each method can be called from other buildout recipes by accessing the option via ${part:method} or in code via self.buildout[part][method].

Offsetting port numbers

The following example will make all the values of ports_base available with an offset added to each one. This example demonstrates the special init option, which enables you to run a special function where the result is not stored against the part within buildout:


recipe = mr.scripty
OFFSET = 1000
init =
    ... for key,value in self.buildout['ports_base'].items():
    ...     self.options[key] = str(int(value)+int(self.OFFSET))

So, the usage of init enables us to create options against the [ports] section using arbitrary code. In the example above, this will result in all of the options under [ports_base] being processed to add the OFFSET value to the port. The end result is that other sections of buildout can now reference ${ports:instance1} and ${ports:instance2}, which will have values of 9101 and 9102 respectively.

Checking existence of directories

This example tests the existence of a list of directories and selects the first one that can be found on the system. In this particular example, we look through a list of potential JDK directories, as the location will differ across Linux distributions, in order to install an egg that depends on having a Java SDK install available:

parts =

recipe = mr.scripty
java =
    ... import os
    ... paths = self.JAVA_PATHS.split('\n')
    ... exists = [os.path.exists(path) for path in paths]
    ... return paths[exists.index(True)]

JAVA_HOME = ${scripty:java}

recipe = zc.recipe.egg:custom
egg = JPype
find-links =
environment = java-env

Contributors”, Dylan Jay

Change history

1.0 (2016-11-16)

  • Add support for Python 3.4. This breaks with Python 2.6 and before. [Sylvain Viollon]

  • Integrate with travis, coveralls - [abdul.maliyakkal]

  • Improve readme [djay]

1.0b3 (2011-12-14)

  • Update documentation with additional examples. [davidjb]

  • fix indenting issues [djay]

  • init is handled as special function where result isn’t stored [djay]

1.0b2 (2011-03-23)

  • Allow constants if option all uppercase [djay]

  • function return values converted to strings or empty string if None [djay]

1.0b1 (2011-03-15)

  • Initial version [“Dylan Jay”, djay]

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