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# -*- coding: utf-8 -*-
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"""Mimic C structs with lots of extra functionality.
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"""
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#*****************************************************************************
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# Copyright (C) 2001-2004 Fernando Perez <fperez@colorado.edu>
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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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__all__ = ['Struct']
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import types
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import pprint
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from IPython.utils.genutils import list2dict2
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class Struct:
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"""Class to mimic C structs but also provide convenient dictionary-like
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functionality.
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Instances can be initialized with a dictionary, a list of key=value pairs
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or both. If both are present, the dictionary must come first.
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Because Python classes provide direct assignment to their members, it's
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easy to overwrite normal methods (S.copy = 1 would destroy access to
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S.copy()). For this reason, all builtin method names are protected and
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can't be assigned to. An attempt to do s.copy=1 or s['copy']=1 will raise
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a KeyError exception. If you really want to, you can bypass this
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protection by directly assigning to __dict__: s.__dict__['copy']=1 will
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still work. Doing this will break functionality, though. As in most of
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Python, namespace protection is weakly enforced, so feel free to shoot
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yourself if you really want to.
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Note that this class uses more memory and is *much* slower than a regular
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dictionary, so be careful in situations where memory or performance are
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critical. But for day to day use it should behave fine. It is particularly
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convenient for storing configuration data in programs.
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+,+=,- and -= are implemented. +/+= do merges (non-destructive updates),
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-/-= remove keys from the original. See the method descripitions.
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This class allows a quick access syntax: both s.key and s['key'] are
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valid. This syntax has a limitation: each 'key' has to be explicitly
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accessed by its original name. The normal s.key syntax doesn't provide
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access to the keys via variables whose values evaluate to the desired
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keys. An example should clarify this:
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Define a dictionary and initialize both with dict and k=v pairs:
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>>> d={'a':1,'b':2}
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>>> s=Struct(d,hi=10,ho=20)
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The return of __repr__ can be used to create a new instance:
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>>> s
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Struct({'__allownew': True, 'a': 1, 'b': 2, 'hi': 10, 'ho': 20})
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Note: the special '__allownew' key is used for internal purposes.
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__str__ (called by print) shows it's not quite a regular dictionary:
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>>> print s
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Struct({'__allownew': True, 'a': 1, 'b': 2, 'hi': 10, 'ho': 20})
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Access by explicitly named key with dot notation:
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>>> s.a
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1
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Or like a dictionary:
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>>> s['a']
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1
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If you want a variable to hold the key value, only dictionary access works:
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>>> key='hi'
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>>> s.key
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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AttributeError: Struct instance has no attribute 'key'
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>>> s[key]
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10
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Another limitation of the s.key syntax (and Struct(key=val)
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initialization): keys can't be numbers. But numeric keys can be used and
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accessed using the dictionary syntax. Again, an example:
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This doesn't work (prompt changed to avoid confusing the test system):
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->> s=Struct(4='hi')
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Traceback (most recent call last):
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...
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SyntaxError: keyword can't be an expression
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But this does:
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>>> s=Struct()
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>>> s[4]='hi'
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>>> s
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Struct({4: 'hi', '__allownew': True})
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>>> s[4]
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'hi'
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"""
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# Attributes to which __setitem__ and __setattr__ will block access.
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# Note: much of this will be moot in Python 2.2 and will be done in a much
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# cleaner way.
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__protected = ('copy dict dictcopy get has_attr has_key items keys '
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'merge popitem setdefault update values '
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'__make_dict __dict_invert ').split()
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def __init__(self,dict=None,**kw):
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"""Initialize with a dictionary, another Struct, or by giving
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explicitly the list of attributes.
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Both can be used, but the dictionary must come first:
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Struct(dict), Struct(k1=v1,k2=v2) or Struct(dict,k1=v1,k2=v2).
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"""
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self.__dict__['__allownew'] = True
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if dict is None:
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dict = {}
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if isinstance(dict,Struct):
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dict = dict.dict()
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elif dict and type(dict) is not types.DictType:
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raise TypeError,\
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'Initialize with a dictionary or key=val pairs.'
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dict.update(kw)
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# do the updating by hand to guarantee that we go through the
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# safety-checked __setitem__
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for k,v in dict.items():
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self[k] = v
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def __setitem__(self,key,value):
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"""Used when struct[key] = val calls are made."""
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if key in Struct.__protected:
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raise KeyError,'Key '+`key`+' is a protected key of class Struct.'
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if not self['__allownew'] and key not in self.__dict__:
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raise KeyError(
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"Can't create unknown attribute %s - Check for typos, or use allow_new_attr to create new attributes!" %
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key)
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self.__dict__[key] = value
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def __setattr__(self, key, value):
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"""Used when struct.key = val calls are made."""
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self.__setitem__(key,value)
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def __str__(self):
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"""Gets called by print."""
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return 'Struct('+ pprint.pformat(self.__dict__)+')'
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def __repr__(self):
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"""Gets called by repr.
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A Struct can be recreated with S_new=eval(repr(S_old))."""
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return self.__str__()
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def __getitem__(self,key):
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"""Allows struct[key] access."""
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return self.__dict__[key]
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def __contains__(self,key):
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"""Allows use of the 'in' operator.
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Examples:
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>>> s = Struct(x=1)
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>>> 'x' in s
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True
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>>> 'y' in s
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False
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>>> s[4] = None
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>>> 4 in s
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True
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>>> s.z = None
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>>> 'z' in s
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True
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"""
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return key in self.__dict__
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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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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 form S and S.merge(S2)"""
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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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"""Return S1-S2, where all keys in S2 have been deleted (if present)
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from S1."""
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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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"""Do in place S = S - S2, meaning all keys in S2 have been deleted
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(if present) from S1."""
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for k in other.keys():
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if self.has_key(k):
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del self.__dict__[k]
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def __make_dict(self,__loc_data__,**kw):
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"Helper function for update and merge. Return a dict from data."
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if __loc_data__ == None:
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dict = {}
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elif type(__loc_data__) is types.DictType:
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dict = __loc_data__
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elif isinstance(__loc_data__,Struct):
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dict = __loc_data__.__dict__
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else:
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raise TypeError, 'Update with a dict, a Struct or key=val pairs.'
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if kw:
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dict.update(kw)
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return dict
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def __dict_invert(self,dict):
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"""Helper function for merge. Takes a dictionary whose values are
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lists and returns a dict. with the elements of each list as keys and
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the original keys as values."""
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outdict = {}
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for k,lst in dict.items():
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if type(lst) is types.StringType:
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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 clear(self):
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"""Clear all attributes."""
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self.__dict__.clear()
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def copy(self):
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"""Return a (shallow) copy of a Struct."""
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return Struct(self.__dict__.copy())
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def dict(self):
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"""Return the Struct's dictionary."""
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return self.__dict__
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def dictcopy(self):
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"""Return a (shallow) copy of the Struct's dictionary."""
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return self.__dict__.copy()
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def popitem(self):
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"""S.popitem() -> (k, v), remove and return some (key, value) pair as
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a 2-tuple; but raise KeyError if S is empty."""
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return self.__dict__.popitem()
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def update(self,__loc_data__=None,**kw):
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"""Update (merge) with data from another Struct or from a dictionary.
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Optionally, one or more key=value pairs can be given at the end for
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direct update."""
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# The funny name __loc_data__ is to prevent a common variable name
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# which could be a fieled of a Struct to collide with this
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# parameter. The problem would arise if the function is called with a
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# keyword with this same name that a user means to add as a Struct
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# field.
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newdict = Struct.__make_dict(self,__loc_data__,**kw)
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for k,v in newdict.iteritems():
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self[k] = v
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def merge(self,__loc_data__=None,__conflict_solve=None,**kw):
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"""S.merge(data,conflict,k=v1,k=v2,...) -> merge data and k=v into S.
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This is similar to update(), but much more flexible. First, a dict is
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made from data+key=value pairs. When merging this dict with the Struct
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S, the optional dictionary 'conflict' is used to decide 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 update method's
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behavior).
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conflict is a dictionary of binary functions which will be used to
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solve key conflicts. It must have the following structure:
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conflict == { fn1 : [Skey1,Skey2,...], fn2 : [Skey3], etc }
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Values must be lists or whitespace separated strings which are
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automatically converted to lists of strings by calling string.split().
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Each key of conflict is a function which defines a policy for
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resolving conflicts when merging with the input data. Each fn must be
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a binary function which returns the desired outcome for a key
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conflict. These functions will be called as fn(old,new).
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An example is probably in order. Suppose you are merging the struct S
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with a dict D and the following conflict policy dict:
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S.merge(D,{fn1:['a','b',4], fn2:'key_c key_d'})
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If the key 'a' is found in both S and D, the merge method will call:
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S['a'] = fn1(S['a'],D['a'])
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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 works for strings!
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You can use those four words (as strings) as keys in conflict 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. That is, the call
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S.merge(D,{'preserve':'a b c','add':[4,5,'d'],my_function:[6]})
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will automatically substitute the functions preserve and add for the
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names 'preserve' and 'add' before making any function calls.
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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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data_dict = Struct.__make_dict(self,__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 = list2dict2(self.keys(),default = 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(Struct.__dict_invert(self,inv_conflict_solve_user))
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#print 'merge. conflict_solve: '; pprint(conflict_solve) # dbg
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#print '*'*50,'in merger. conflict_solver:'; pprint(conflict_solve)
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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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def has_key(self,key):
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"""Like has_key() dictionary method."""
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return self.__dict__.has_key(key)
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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, to make sure that all available keys in the
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internal dictionary of the Struct appear also as attributes (even
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numeric keys)."""
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return self.__dict__.has_key(key)
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def items(self):
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"""Return the items in the Struct's dictionary, in the same format
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as a call to {}.items()."""
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return self.__dict__.items()
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def keys(self):
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"""Return the keys in the Struct's dictionary, in the same format
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as a call to {}.keys()."""
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return self.__dict__.keys()
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def values(self,keys=None):
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"""Return the values in the Struct's dictionary, in the same format
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as a call to {}.values().
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Can be called with an optional argument keys, which must be a list or
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tuple of keys. In this case it returns only the values corresponding
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to those keys (allowing a form of 'slicing' for Structs)."""
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if not keys:
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return self.__dict__.values()
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else:
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ret=[]
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for k in keys:
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ret.append(self[k])
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return ret
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def get(self,attr,val=None):
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"""S.get(k[,d]) -> S[k] if k in S, else d. d defaults to None."""
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try:
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return self[attr]
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except KeyError:
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return val
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def setdefault(self,attr,val=None):
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"""S.setdefault(k[,d]) -> S.get(k,d), also set S[k]=d if k not in S"""
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if not self.has_key(attr):
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self[attr] = val
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return self.get(attr,val)
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def allow_new_attr(self, allow = True):
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""" Set whether new attributes can be created inside 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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self['__allownew'] = allow
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# end class Struct
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