require.distro.package about fabtools

[ronnix]

Yes, I've been thinking about adding this kind of layer.

One issue that we need to address is that package names may vary from one distro to another. See the implementation of require.git.command() for example.

I'd like the API to keep the common case simple, but allow the user to override the default package name with alternate names for given distros / families. Something like:

# Simple case
require.system.package('python-dev')

# System-specific overrides
require.system.package('git', debian='git-core', sun='scmgit-base')

For installing multiple packages, each list item could be either a string or a dictionary, but it's not as pretty:

require.system.packages([
    'curl',
    'python-dev',
    {'default': 'git', 'debian': 'git-core', 'sun': 'scmgit-base'},
])

[ponty]

The same concept with less magic:

def choose_by_distrib_family(default, **kwargs):
    return dict(**kwargs).get(distrib_family(), default)

# Simple case
require.system.package(
    choose_by_distrib_family('git', debian='git-core', sun='scmgit-base'))

# multiple packages
require.system.packages([
    'curl',
    'python-dev',
    choose_by_distrib_family(default='git', debian='git-core', sun='scmgit-base'),
])

[ronnix]

Nice! Make it shorter maybe (by_distrib_family)?

[ronnix]

Also, we may want to cache the result of distrib_family()...

[ponty]

Most of the functions in system.py can be cached, but this should be a new ticket.

This could be implemented using memoization.

Original code:
http://stackoverflow.com/questions/1988804/what-is-memoization-and-how-can-i-use-it-in-python

Modified with env.host

def memoize(fn):
    """returns a memoized version of any function that can be called
    with the same list of arguments.
    Usage: foo = memoize(foo)"""

    def foo(*args, **kwargs):
        items = tuple(sorted(kwargs.items()))
        if (args, items, env.host) not in foo.past_calls:
            foo.past_calls[(args, items, env.host)] = fn(*args,**kwargs)
        return foo.past_calls[(args, items, env.host)]
    foo.past_calls = dict([])
    foo.__name__ = 'memoized_' + fn.__name__ 
    return foo

@memoize
def distrib_family():
    """
    """

[nicfit]

Where does this stand? I've created something similar in my tree.

Also, memoize cache would need to be cleared for each host change. e.g.,
fab -H centos_host, debian_host deploy

[ponty]

I didn't implemented it yet.

[deronnax]

no news ? I was thinking, something like a json file with a map between package canonical name and its name in the different OS would be awesome. When doing a require.package, fabtools would check in the file if the package in present, and use the package name.
The file would be bundled with fabtools with a name like packages_name_map.json, and the user could override it in various ways. Thanks to the json format, to change it or correct it, even a no-programmer can edit it.

For git, it would be:

[ {"git": {"debian": "git-core", "sun" : "git-scm", "gentoo": "git-scm"}}]