# -*- coding: utf-8 -*- """Mimic C structs with lots of extra functionality. $Id: ipstruct.py 1005 2006-01-12 08:39:26Z fperez $""" #***************************************************************************** # Copyright (C) 2001-2004 Fernando Perez # # Distributed under the terms of the BSD License. The full license is in # the file COPYING, distributed as part of this software. #***************************************************************************** from IPython import Release __author__ = '%s <%s>' % Release.authors['Fernando'] __license__ = Release.license __all__ = ['Struct'] import types from IPython.genutils import list2dict2 class Struct: """Class to mimic C structs but also provide convenient dictionary-like functionality. Instances can be initialized with a dictionary, a list of key=value pairs or both. If both are present, the dictionary must come first. Because Python classes provide direct assignment to their members, it's easy to overwrite normal methods (S.copy = 1 would destroy access to S.copy()). For this reason, all builtin method names are protected and can't be assigned to. An attempt to do s.copy=1 or s['copy']=1 will raise a KeyError exception. If you really want to, you can bypass this protection by directly assigning to __dict__: s.__dict__['copy']=1 will still work. Doing this will break functionality, though. As in most of Python, namespace protection is weakly enforced, so feel free to shoot yourself if you really want to. Note that this class uses more memory and is *much* slower than a regular dictionary, so be careful in situations where memory or performance are critical. But for day to day use it should behave fine. It is particularly convenient for storing configuration data in programs. +,+=,- and -= are implemented. +/+= do merges (non-destructive updates), -/-= remove keys from the original. See the method descripitions. This class allows a quick access syntax: both s.key and s['key'] are valid. This syntax has a limitation: each 'key' has to be explicitly accessed by its original name. The normal s.key syntax doesn't provide access to the keys via variables whose values evaluate to the desired keys. An example should clarify this: Define a dictionary and initialize both with dict and k=v pairs: >>> d={'a':1,'b':2} >>> s=Struct(d,hi=10,ho=20) The return of __repr__ can be used to create a new instance: >>> s Struct({'ho': 20, 'b': 2, 'hi': 10, 'a': 1}) __str__ (called by print) shows it's not quite a regular dictionary: >>> print s Struct {a: 1, b: 2, hi: 10, ho: 20} Access by explicitly named key with dot notation: >>> s.a 1 Or like a dictionary: >>> s['a'] 1 If you want a variable to hold the key value, only dictionary access works: >>> key='hi' >>> s.key Traceback (most recent call last): File "", line 1, in ? AttributeError: Struct instance has no attribute 'key' >>> s[key] 10 Another limitation of the s.key syntax (and Struct(key=val) initialization): keys can't be numbers. But numeric keys can be used and accessed using the dictionary syntax. Again, an example: This doesn't work: >>> s=Struct(4='hi') SyntaxError: keyword can't be an expression But this does: >>> s=Struct() >>> s[4]='hi' >>> s Struct({4: 'hi'}) >>> s[4] 'hi' """ # Attributes to which __setitem__ and __setattr__ will block access. # Note: much of this will be moot in Python 2.2 and will be done in a much # cleaner way. __protected = ('copy dict dictcopy get has_attr has_key items keys ' 'merge popitem setdefault update values ' '__make_dict __dict_invert ').split() def __init__(self,dict=None,**kw): """Initialize with a dictionary, another Struct, or by giving explicitly the list of attributes. Both can be used, but the dictionary must come first: Struct(dict), Struct(k1=v1,k2=v2) or Struct(dict,k1=v1,k2=v2). """ if dict is None: dict = {} if isinstance(dict,Struct): dict = dict.dict() elif dict and type(dict) is not types.DictType: raise TypeError,\ 'Initialize with a dictionary or key=val pairs.' dict.update(kw) # do the updating by hand to guarantee that we go through the # safety-checked __setitem__ for k,v in dict.items(): self[k] = v def __setitem__(self,key,value): """Used when struct[key] = val calls are made.""" if key in Struct.__protected: raise KeyError,'Key '+`key`+' is a protected key of class Struct.' self.__dict__[key] = value def __setattr__(self, key, value): """Used when struct.key = val calls are made.""" self.__setitem__(key,value) def __str__(self): """Gets called by print.""" return 'Struct('+str(self.__dict__)+')' def __repr__(self): """Gets called by repr. A Struct can be recreated with S_new=eval(repr(S_old)).""" return 'Struct('+str(self.__dict__)+')' def __getitem__(self,key): """Allows struct[key] access.""" return self.__dict__[key] def __contains__(self,key): """Allows use of the 'in' operator.""" return self.__dict__.has_key(key) def __iadd__(self,other): """S += S2 is a shorthand for S.merge(S2).""" self.merge(other) return self def __add__(self,other): """S + S2 -> New Struct made form S and S.merge(S2)""" Sout = self.copy() Sout.merge(other) return Sout def __sub__(self,other): """Return S1-S2, where all keys in S2 have been deleted (if present) from S1.""" Sout = self.copy() Sout -= other return Sout def __isub__(self,other): """Do in place S = S - S2, meaning all keys in S2 have been deleted (if present) from S1.""" for k in other.keys(): if self.has_key(k): del self.__dict__[k] def __make_dict(self,__loc_data__,**kw): "Helper function for update and merge. Return a dict from data." if __loc_data__ == None: dict = {} elif type(__loc_data__) is types.DictType: dict = __loc_data__ elif isinstance(__loc_data__,Struct): dict = __loc_data__.__dict__ else: raise TypeError, 'Update with a dict, a Struct or key=val pairs.' if kw: dict.update(kw) return dict def __dict_invert(self,dict): """Helper function for merge. Takes a dictionary whose values are lists and returns a dict. with the elements of each list as keys and the original keys as values.""" outdict = {} for k,lst in dict.items(): if type(lst) is types.StringType: lst = lst.split() for entry in lst: outdict[entry] = k return outdict def clear(self): """Clear all attributes.""" self.__dict__.clear() def copy(self): """Return a (shallow) copy of a Struct.""" return Struct(self.__dict__.copy()) def dict(self): """Return the Struct's dictionary.""" return self.__dict__ def dictcopy(self): """Return a (shallow) copy of the Struct's dictionary.""" return self.__dict__.copy() def popitem(self): """S.popitem() -> (k, v), remove and return some (key, value) pair as a 2-tuple; but raise KeyError if S is empty.""" return self.__dict__.popitem() def update(self,__loc_data__=None,**kw): """Update (merge) with data from another Struct or from a dictionary. Optionally, one or more key=value pairs can be given at the end for direct update.""" # The funny name __loc_data__ is to prevent a common variable name which # could be a fieled of a Struct to collide with this parameter. The problem # would arise if the function is called with a keyword with this same name # that a user means to add as a Struct field. newdict = Struct.__make_dict(self,__loc_data__,**kw) for k,v in newdict.items(): self[k] = v def merge(self,__loc_data__=None,__conflict_solve=None,**kw): """S.merge(data,conflict,k=v1,k=v2,...) -> merge data and k=v into S. This is similar to update(), but much more flexible. First, a dict is made from data+key=value pairs. When merging this dict with the Struct S, the optional dictionary 'conflict' is used to decide what to do. If conflict is not given, the default behavior is to preserve any keys with their current value (the opposite of the update method's behavior). conflict is a dictionary of binary functions which will be used to solve key conflicts. It must have the following structure: conflict == { fn1 : [Skey1,Skey2,...], fn2 : [Skey3], etc } Values must be lists or whitespace separated strings which are automatically converted to lists of strings by calling string.split(). Each key of conflict is a function which defines a policy for resolving conflicts when merging with the input data. Each fn must be a binary function which returns the desired outcome for a key conflict. These functions will be called as fn(old,new). An example is probably in order. Suppose you are merging the struct S with a dict D and the following conflict policy dict: S.merge(D,{fn1:['a','b',4], fn2:'key_c key_d'}) If the key 'a' is found in both S and D, the merge method will call: S['a'] = fn1(S['a'],D['a']) As a convenience, merge() provides five (the most commonly needed) pre-defined policies: preserve, update, add, add_flip and add_s. The easiest explanation is their implementation: preserve = lambda old,new: old update = lambda old,new: new add = lambda old,new: old + new add_flip = lambda old,new: new + old # note change of order! add_s = lambda old,new: old + ' ' + new # only works for strings! You can use those four words (as strings) as keys in conflict instead of defining them as functions, and the merge method will substitute the appropriate functions for you. That is, the call S.merge(D,{'preserve':'a b c','add':[4,5,'d'],my_function:[6]}) will automatically substitute the functions preserve and add for the names 'preserve' and 'add' before making any function calls. For more complicated conflict resolution policies, you still need to construct your own functions. """ data_dict = Struct.__make_dict(self,__loc_data__,**kw) # policies for conflict resolution: two argument functions which return # the value that will go in the new struct preserve = lambda old,new: old update = lambda old,new: new add = lambda old,new: old + new add_flip = lambda old,new: new + old # note change of order! add_s = lambda old,new: old + ' ' + new # default policy is to keep current keys when there's a conflict conflict_solve = list2dict2(self.keys(),default = preserve) # the conflict_solve dictionary is given by the user 'inverted': we # need a name-function mapping, it comes as a function -> names # dict. Make a local copy (b/c we'll make changes), replace user # strings for the three builtin policies and invert it. if __conflict_solve: inv_conflict_solve_user = __conflict_solve.copy() for name, func in [('preserve',preserve), ('update',update), ('add',add), ('add_flip',add_flip), ('add_s',add_s)]: if name in inv_conflict_solve_user.keys(): inv_conflict_solve_user[func] = inv_conflict_solve_user[name] del inv_conflict_solve_user[name] conflict_solve.update(Struct.__dict_invert(self,inv_conflict_solve_user)) #print 'merge. conflict_solve: '; pprint(conflict_solve) # dbg #print '*'*50,'in merger. conflict_solver:'; pprint(conflict_solve) for key in data_dict: if key not in self: self[key] = data_dict[key] else: self[key] = conflict_solve[key](self[key],data_dict[key]) def has_key(self,key): """Like has_key() dictionary method.""" return self.__dict__.has_key(key) def hasattr(self,key): """hasattr function available as a method. Implemented like has_key, to make sure that all available keys in the internal dictionary of the Struct appear also as attributes (even numeric keys).""" return self.__dict__.has_key(key) def items(self): """Return the items in the Struct's dictionary, in the same format as a call to {}.items().""" return self.__dict__.items() def keys(self): """Return the keys in the Struct's dictionary, in the same format as a call to {}.keys().""" return self.__dict__.keys() def values(self,keys=None): """Return the values in the Struct's dictionary, in the same format as a call to {}.values(). Can be called with an optional argument keys, which must be a list or tuple of keys. In this case it returns only the values corresponding to those keys (allowing a form of 'slicing' for Structs).""" if not keys: return self.__dict__.values() else: ret=[] for k in keys: ret.append(self[k]) return ret def get(self,attr,val=None): """S.get(k[,d]) -> S[k] if S.has_key(k), else d. d defaults to None.""" try: return self[attr] except KeyError: return val def setdefault(self,attr,val=None): """S.setdefault(k[,d]) -> S.get(k,d), also set S[k]=d if not S.has_key(k)""" if not self.has_key(attr): self[attr] = val return self.get(attr,val) # end class Struct