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380 lines
12 KiB
Python
380 lines
12 KiB
Python
# encoding: utf-8
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"""A dict subclass that supports attribute style access.
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Authors:
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* Fernando Perez (original)
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* Brian Granger (refactoring to a dict subclass)
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"""
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#-----------------------------------------------------------------------------
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# Copyright (C) 2008-2011 The IPython Development Team
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#
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# Distributed under the terms of the BSD License. The full license is in
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# the file COPYING, distributed as part of this software.
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#-----------------------------------------------------------------------------
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#-----------------------------------------------------------------------------
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# Imports
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#-----------------------------------------------------------------------------
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__all__ = ['Struct']
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#-----------------------------------------------------------------------------
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# Code
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#-----------------------------------------------------------------------------
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class Struct(dict):
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"""A dict subclass with attribute style access.
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This dict subclass has a a few extra features:
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* Attribute style access.
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* Protection of class members (like keys, items) when using attribute
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style access.
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* The ability to restrict assignment to only existing keys.
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* Intelligent merging.
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* Overloaded operators.
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"""
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_allownew = True
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def __init__(self, *args, **kw):
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"""Initialize with a dictionary, another Struct, or data.
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Parameters
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----------
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*args : dict, Struct
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Initialize with one dict or Struct
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**kw : dict
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Initialize with key, value pairs.
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Examples
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--------
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>>> s = Struct(a=10,b=30)
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>>> s.a
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10
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>>> s.b
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30
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>>> s2 = Struct(s,c=30)
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>>> sorted(s2.keys())
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['a', 'b', 'c']
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"""
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object.__setattr__(self, '_allownew', True)
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dict.__init__(self, *args, **kw)
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def __setitem__(self, key, value):
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"""Set an item with check for allownew.
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Examples
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--------
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>>> s = Struct()
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>>> s['a'] = 10
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>>> s.allow_new_attr(False)
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>>> s['a'] = 10
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>>> s['a']
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10
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>>> try:
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... s['b'] = 20
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... except KeyError:
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... print('this is not allowed')
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...
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this is not allowed
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"""
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if not self._allownew and key not in self:
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raise KeyError(
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"can't create new attribute %s when allow_new_attr(False)" % key)
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dict.__setitem__(self, key, value)
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def __setattr__(self, key, value):
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"""Set an attr with protection of class members.
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This calls :meth:`self.__setitem__` but convert :exc:`KeyError` to
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:exc:`AttributeError`.
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Examples
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--------
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>>> s = Struct()
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>>> s.a = 10
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>>> s.a
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10
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>>> try:
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... s.get = 10
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... except AttributeError:
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... print("you can't set a class member")
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...
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you can't set a class member
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"""
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# If key is an str it might be a class member or instance var
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if isinstance(key, str):
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# I can't simply call hasattr here because it calls getattr, which
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# calls self.__getattr__, which returns True for keys in
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# self._data. But I only want keys in the class and in
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# self.__dict__
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if key in self.__dict__ or hasattr(Struct, key):
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raise AttributeError(
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'attr %s is a protected member of class Struct.' % key
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)
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try:
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self.__setitem__(key, value)
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except KeyError as e:
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raise AttributeError(e) from e
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def __getattr__(self, key):
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"""Get an attr by calling :meth:`dict.__getitem__`.
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Like :meth:`__setattr__`, this method converts :exc:`KeyError` to
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:exc:`AttributeError`.
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Examples
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--------
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>>> s = Struct(a=10)
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>>> s.a
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10
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>>> type(s.get)
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<...method'>
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>>> try:
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... s.b
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... except AttributeError:
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... print("I don't have that key")
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...
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I don't have that key
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"""
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try:
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result = self[key]
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except KeyError as e:
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raise AttributeError(key) from e
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else:
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return result
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def __iadd__(self, other):
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"""s += s2 is a shorthand for s.merge(s2).
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Examples
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--------
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>>> s = Struct(a=10,b=30)
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>>> s2 = Struct(a=20,c=40)
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>>> s += s2
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>>> sorted(s.keys())
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['a', 'b', 'c']
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"""
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self.merge(other)
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return self
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def __add__(self,other):
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"""s + s2 -> New Struct made from s.merge(s2).
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Examples
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--------
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>>> s1 = Struct(a=10,b=30)
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>>> s2 = Struct(a=20,c=40)
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>>> s = s1 + s2
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>>> sorted(s.keys())
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['a', 'b', 'c']
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"""
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sout = self.copy()
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sout.merge(other)
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return sout
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def __sub__(self,other):
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"""s1 - s2 -> remove keys in s2 from s1.
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Examples
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--------
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>>> s1 = Struct(a=10,b=30)
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>>> s2 = Struct(a=40)
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>>> s = s1 - s2
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>>> s
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{'b': 30}
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"""
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sout = self.copy()
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sout -= other
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return sout
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def __isub__(self,other):
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"""Inplace remove keys from self that are in other.
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Examples
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--------
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>>> s1 = Struct(a=10,b=30)
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>>> s2 = Struct(a=40)
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>>> s1 -= s2
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>>> s1
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{'b': 30}
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"""
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for k in other.keys():
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if k in self:
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del self[k]
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return self
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def __dict_invert(self, data):
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"""Helper function for merge.
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Takes a dictionary whose values are lists and returns a dict with
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the elements of each list as keys and the original keys as values.
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"""
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outdict = {}
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for k,lst in data.items():
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if isinstance(lst, str):
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lst = lst.split()
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for entry in lst:
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outdict[entry] = k
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return outdict
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def dict(self):
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return self
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def copy(self):
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"""Return a copy as a Struct.
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Examples
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--------
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>>> s = Struct(a=10,b=30)
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>>> s2 = s.copy()
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>>> type(s2) is Struct
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True
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"""
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return Struct(dict.copy(self))
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def hasattr(self, key):
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"""hasattr function available as a method.
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Implemented like has_key.
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Examples
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--------
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>>> s = Struct(a=10)
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>>> s.hasattr('a')
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True
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>>> s.hasattr('b')
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False
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>>> s.hasattr('get')
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False
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"""
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return key in self
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def allow_new_attr(self, allow = True):
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"""Set whether new attributes can be created in this Struct.
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This can be used to catch typos by verifying that the attribute user
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tries to change already exists in this Struct.
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"""
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object.__setattr__(self, '_allownew', allow)
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def merge(self, __loc_data__=None, __conflict_solve=None, **kw):
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"""Merge two Structs with customizable conflict resolution.
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This is similar to :meth:`update`, but much more flexible. First, a
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dict is made from data+key=value pairs. When merging this dict with
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the Struct S, the optional dictionary 'conflict' is used to decide
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what to do.
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If conflict is not given, the default behavior is to preserve any keys
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with their current value (the opposite of the :meth:`update` method's
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behavior).
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Parameters
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----------
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__loc_data__ : dict, Struct
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The data to merge into self
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__conflict_solve : dict
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The conflict policy dict. The keys are binary functions used to
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resolve the conflict and the values are lists of strings naming
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the keys the conflict resolution function applies to. Instead of
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a list of strings a space separated string can be used, like
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'a b c'.
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**kw : dict
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Additional key, value pairs to merge in
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Notes
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-----
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The `__conflict_solve` dict is a dictionary of binary functions which will be used to
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solve key conflicts. Here is an example::
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__conflict_solve = dict(
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func1=['a','b','c'],
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func2=['d','e']
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)
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In this case, the function :func:`func1` will be used to resolve
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keys 'a', 'b' and 'c' and the function :func:`func2` will be used for
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keys 'd' and 'e'. This could also be written as::
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__conflict_solve = dict(func1='a b c',func2='d e')
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These functions will be called for each key they apply to with the
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form::
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func1(self['a'], other['a'])
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The return value is used as the final merged value.
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As a convenience, merge() provides five (the most commonly needed)
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pre-defined policies: preserve, update, add, add_flip and add_s. The
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easiest explanation is their implementation::
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preserve = lambda old,new: old
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update = lambda old,new: new
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add = lambda old,new: old + new
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add_flip = lambda old,new: new + old # note change of order!
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add_s = lambda old,new: old + ' ' + new # only for str!
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You can use those four words (as strings) as keys instead
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of defining them as functions, and the merge method will substitute
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the appropriate functions for you.
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For more complicated conflict resolution policies, you still need to
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construct your own functions.
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Examples
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--------
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This show the default policy:
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>>> s = Struct(a=10,b=30)
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>>> s2 = Struct(a=20,c=40)
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>>> s.merge(s2)
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>>> sorted(s.items())
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[('a', 10), ('b', 30), ('c', 40)]
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Now, show how to specify a conflict dict:
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>>> s = Struct(a=10,b=30)
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>>> s2 = Struct(a=20,b=40)
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>>> conflict = {'update':'a','add':'b'}
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>>> s.merge(s2,conflict)
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>>> sorted(s.items())
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[('a', 20), ('b', 70)]
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"""
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data_dict = dict(__loc_data__,**kw)
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# policies for conflict resolution: two argument functions which return
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# the value that will go in the new struct
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preserve = lambda old,new: old
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update = lambda old,new: new
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add = lambda old,new: old + new
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add_flip = lambda old,new: new + old # note change of order!
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add_s = lambda old,new: old + ' ' + new
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# default policy is to keep current keys when there's a conflict
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conflict_solve = dict.fromkeys(self, preserve)
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# the conflict_solve dictionary is given by the user 'inverted': we
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# need a name-function mapping, it comes as a function -> names
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# dict. Make a local copy (b/c we'll make changes), replace user
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# strings for the three builtin policies and invert it.
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if __conflict_solve:
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inv_conflict_solve_user = __conflict_solve.copy()
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for name, func in [('preserve',preserve), ('update',update),
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('add',add), ('add_flip',add_flip),
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('add_s',add_s)]:
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if name in inv_conflict_solve_user.keys():
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inv_conflict_solve_user[func] = inv_conflict_solve_user[name]
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del inv_conflict_solve_user[name]
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conflict_solve.update(self.__dict_invert(inv_conflict_solve_user))
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for key in data_dict:
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if key not in self:
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self[key] = data_dict[key]
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else:
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self[key] = conflict_solve[key](self[key],data_dict[key])
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