cfg.py

   1 """A simple wrapper around optparse and configobj
   2
   3 >>> from cfg import o, setup_cfg
   4 >>> cfg = setup_cfg([
   5             o('-c', '--conf', dest='conf',
   6               help='Configuration file'),
   7               ...
   8               ], {'foo':  34})
   9 >>> print cfg['bar.yaht']
  10 ...
  11 """
  12
  13 from os.path import dirname, abspath
  14
  15 import configobj
  16 from optparse  import make_option as o, OptionParser
  17
  18 # Global 'cfg' object
  19 cfg = None
  20
  21 # ConfigObj does not support passing custom template variables like in
  22 # most HTML templating systems. This is bad.
  23 # ConfigObj code is also not very extensible. This is very bad.
  24 # So we hack around the `interpolation_engines` global variable to
  25 # get our job done.
  26
  27 def configobj_namespace(namespace):
  28     global configobj
  29     import re
  30
  31     class GoodConfigParserInterpolation(configobj.ConfigParserInterpolation):
  32         """Resolve custom template variables manually passed"""
  33
  34         def interpolate(self, key, value):
  35             try:
  36                 return super(GoodConfigParserInterpolation,
  37                              self).interpolate(key, value)
  38             except configobj.InterpolationError:
  39                 # eg: extract 'var' out of '%(var)s'
  40                 match = self._KEYCRE.search(value)
  41                 if match:
  42                     var = match.group(1)
  43                     if var in namespace:
  44                         return re.sub(self._KEYCRE, namespace[var], value)
  45                 raise
  46
  47     # There is another engine 'template' which, for me, never seems to
  48     # work. voidspace?
  49     configobj.interpolation_engines['configparser'] = \
  50         GoodConfigParserInterpolation
  51
  52
  53 def married(options, configobj):
  54     """
  55     Marry optparse and configobj
  56     http://wiki.python.org/moin/ConfigParserShootout
  57     """
  58
  59     class sex(object):
  60
  61         def __setitem__(self, item, value):
  62             return setattr(options, item, value)
  63
  64         def __getitem__(self, item):
  65             # If `item` is not found in `options` read from `configobj`
  66             try:
  67                 value = getattr(options, item)
  68                 if value is None:
  69                     raise AttributeError
  70                 else:
  71                     return value
  72             except AttributeError:
  73                 c = configobj
  74                 try:
  75                     for a in item.split('.'):
  76                         c = c[a]
  77                 except KeyError:
  78                     return None # optparse, too, returns None in this case.
  79                 return c
  80
  81         def __str__(self):
  82             return "<cfg {\n%s,\n\n%s\n}>" % (options, configobj)
  83
  84     return sex()
  85
  86 def setup_cfg(option_list, defaults, namespace={}):
  87     global cfg
  88
  89     oparser = OptionParser(option_list=option_list)
  90     oparser.set_defaults(**defaults)
  91     (options, args) = oparser.parse_args()
  92
  93     if options.conf is None:
  94         raise SystemExit, "You must specify the --conf option."
  95
  96     # `pwd` contains the directory where the conf file lies.
  97     namespace['pwd'] = abspath(dirname(abspath(options.conf)))
  98
  99     # patch it!
 100     configobj_namespace(namespace)
 101
 102     cobj = configobj.ConfigObj(options.conf)
 103     cfg = married(options, cobj)
 104     return cfg
 105
 106 __all__ = ['setup_cfg', 'o', 'cfg']