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ssamson-tis
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class ConfigNamespace(object):
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"""Abstract class representing the interface of Config objects.
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A ConfigNamespace is a collection of names mapped to values, where
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the values may be nested namespaces. Values can be accessed via
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container notation - obj[key] - or via dotted notation - obj.key.
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Both these access methods are equivalent.
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To minimize name conflicts between namespace keys and class members,
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the number of class members should be minimized, and the names of
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all class members should start with an underscore.
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Subclasses must implement the methods for container-like access,
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and this class will automatically provide dotted access.
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"""
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# Methods that must be implemented by subclasses
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def _getitem(self, key):
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return NotImplementedError(key)
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def __setitem__(self, key, value):
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raise NotImplementedError(key, value)
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def __delitem__(self, key):
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raise NotImplementedError(key)
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def __iter__(self):
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return NotImplementedError()
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def _new_namespace(self, name):
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raise NotImplementedError(name)
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def __contains__(self, key):
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try:
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self._getitem(key)
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except KeyError:
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return False
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return True
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# Machinery for converting dotted access into container access,
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# and automatically creating new sections/namespaces.
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#
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# To distinguish between accesses of class members and namespace
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# keys, we first call object.__getattribute__(). If that succeeds,
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# the name is assumed to be a class member. Otherwise it is
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# treated as a namespace key.
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#
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# Therefore, member variables should be defined in the class,
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# not just in the __init__() function. See BasicNamespace for
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# an example.
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def __getitem__(self, key):
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try:
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return self._getitem(key)
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except KeyError:
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return Undefined(key, self)
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def __getattr__(self, name):
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try:
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return self._getitem(name)
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except KeyError:
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if name.startswith('__') and name.endswith('__'):
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raise AttributeError
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return Undefined(name, self)
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def __setattr__(self, name, value):
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try:
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object.__getattribute__(self, name)
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object.__setattr__(self, name, value)
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except AttributeError:
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self.__setitem__(name, value)
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def __delattr__(self, name):
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try:
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object.__getattribute__(self, name)
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object.__delattr__(self, name)
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except AttributeError:
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self.__delitem__(name)
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# During unpickling, Python checks if the class has a __setstate__
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# method. But, the data dicts have not been initialised yet, which
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# leads to _getitem and hence __getattr__ raising an exception. So
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# we explicitly impement default __setstate__ behavior.
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def __setstate__(self, state):
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self.__dict__.update(state)
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class Undefined(object):
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"""Helper class used to hold undefined names until assignment.
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This class helps create any undefined subsections when an
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assignment is made to a nested value. For example, if the
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statement is "cfg.a.b.c = 42", but "cfg.a.b" does not exist yet.
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"""
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def __init__(self, name, namespace):
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object.__setattr__(self, 'name', name)
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object.__setattr__(self, 'namespace', namespace)
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def __setattr__(self, name, value):
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obj = self.namespace._new_namespace(self.name)
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obj[name] = value
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def __setitem__(self, name, value):
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obj = self.namespace._new_namespace(self.name)
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obj[name] = value
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# ---- Basic implementation of a ConfigNamespace
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class BasicConfig(ConfigNamespace):
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"""Represents a hierarchical collection of named values.
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Values are added using dotted notation:
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>>> n = BasicConfig()
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>>> n.x = 7
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>>> n.name.first = 'paramjit'
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>>> n.name.last = 'oberoi'
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...and accessed the same way, or with [...]:
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>>> n.x
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7
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>>> n.name.first
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'paramjit'
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>>> n.name.last
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'oberoi'
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>>> n['x']
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7
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>>> n['name']['first']
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'paramjit'
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Iterating over the namespace object returns the keys:
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>>> l = list(n)
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>>> l.sort()
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>>> l
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['name', 'x']
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Values can be deleted using 'del' and printed using 'print'.
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>>> n.aaa = 42
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>>> del n.x
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>>> print n
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aaa = 42
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name.first = paramjit
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name.last = oberoi
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Nested namepsaces are also namespaces:
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>>> isinstance(n.name, ConfigNamespace)
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True
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>>> print n.name
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first = paramjit
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last = oberoi
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>>> sorted(list(n.name))
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['first', 'last']
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Finally, values can be read from a file as follows:
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>>> from StringIO import StringIO
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>>> sio = StringIO('''
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... # comment
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... ui.height = 100
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... ui.width = 150
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... complexity = medium
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... have_python
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... data.secret.password = goodness=gracious me
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... ''')
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>>> n = BasicConfig()
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>>> n._readfp(sio)
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>>> print n
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complexity = medium
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data.secret.password = goodness=gracious me
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have_python
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ui.height = 100
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ui.width = 150
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"""
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# this makes sure that __setattr__ knows this is not a namespace key
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_data = None
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def __init__(self):
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self._data = {}
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def _getitem(self, key):
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return self._data[key]
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def __setitem__(self, key, value):
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self._data[key] = value
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def __delitem__(self, key):
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del self._data[key]
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def __iter__(self):
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return iter(self._data)
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def __str__(self, prefix=''):
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lines = []
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keys = self._data.keys()
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keys.sort()
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for name in keys:
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value = self._data[name]
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if isinstance(value, ConfigNamespace):
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lines.append(value.__str__(prefix='%s%s.' % (prefix,name)))
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else:
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if value is None:
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lines.append('%s%s' % (prefix, name))
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else:
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lines.append('%s%s = %s' % (prefix, name, value))
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return '\n'.join(lines)
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def _new_namespace(self, name):
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obj = BasicConfig()
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self._data[name] = obj
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return obj
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def _readfp(self, fp):
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while True:
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line = fp.readline()
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if not line:
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break
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line = line.strip()
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if not line: continue
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if line[0] == '#': continue
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data = line.split('=', 1)
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if len(data) == 1:
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name = line
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value = None
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else:
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name = data[0].strip()
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value = data[1].strip()
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name_components = name.split('.')
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ns = self
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for n in name_components[:-1]:
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if n in ns:
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ns = ns[n]
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if not isinstance(ns, ConfigNamespace):
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raise TypeError('value-namespace conflict', n)
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else:
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ns = ns._new_namespace(n)
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ns[name_components[-1]] = value
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# ---- Utility functions
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def update_config(target, source):
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"""Imports values from source into target.
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Recursively walks the <source> ConfigNamespace and inserts values
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into the <target> ConfigNamespace. For example:
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>>> n = BasicConfig()
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>>> n.playlist.expand_playlist = True
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>>> n.ui.display_clock = True
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>>> n.ui.display_qlength = True
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>>> n.ui.width = 150
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>>> print n
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playlist.expand_playlist = True
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ui.display_clock = True
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ui.display_qlength = True
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ui.width = 150
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>>> from iniparse import ini
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>>> i = ini.INIConfig()
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>>> update_config(i, n)
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>>> print i
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[playlist]
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expand_playlist = True
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<BLANKLINE>
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[ui]
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display_clock = True
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display_qlength = True
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width = 150
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"""
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for name in source:
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value = source[name]
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if isinstance(value, ConfigNamespace):
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if name in target:
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myns = target[name]
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if not isinstance(myns, ConfigNamespace):
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raise TypeError('value-namespace conflict')
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else:
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myns = target._new_namespace(name)
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update_config(myns, value)
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else:
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target[name] = value
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