smartdict.py revision 6997:5af4976c17e2 
1# Copyright (c) 2005 The Regents of The University of Michigan
2# All rights reserved.
3#
4# Redistribution and use in source and binary forms, with or without
5# modification, are permitted provided that the following conditions are
6# met: redistributions of source code must retain the above copyright
7# notice, this list of conditions and the following disclaimer;
8# redistributions in binary form must reproduce the above copyright
9# notice, this list of conditions and the following disclaimer in the
10# documentation and/or other materials provided with the distribution;
11# neither the name of the copyright holders nor the names of its
12# contributors may be used to endorse or promote products derived from
13# this software without specific prior written permission.
14#
15# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
18# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
19# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
20# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
21# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
25# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26#
27# Authors: Nathan Binkert
28
29# The SmartDict class fixes a couple of issues with using the content
30# of os.environ or similar dicts of strings as Python variables:
31#
32# 1) Undefined variables should return False rather than raising KeyError.
33#
34# 2) String values of 'False', '0', etc., should evaluate to False
35#    (not just the empty string).
36#
37# #1 is solved by overriding __getitem__, and #2 is solved by using a
38# proxy class for values and overriding __nonzero__ on the proxy.
39# Everything else is just to (a) make proxies behave like normal
40# values otherwise, (b) make sure any dict operation returns a proxy
41# rather than a normal value, and (c) coerce values written to the
42# dict to be strings.
43
44
45from convert import *
46from attrdict import attrdict
47
48class Variable(str):
49    """Intelligent proxy class for SmartDict.  Variable will use the
50    various convert functions to attempt to convert values to useable
51    types"""
52    def __int__(self):
53        return toInteger(str(self))
54    def __long__(self):
55        return toLong(str(self))
56    def __float__(self):
57        return toFloat(str(self))
58    def __nonzero__(self):
59        return toBool(str(self))
60    def convert(self, other):
61        t = type(other)
62        if t == bool:
63            return bool(self)
64        if t == int:
65            return int(self)
66        if t == long:
67            return long(self)
68        if t == float:
69            return float(self)
70        return str(self)
71    def __lt__(self, other):
72        return self.convert(other) < other
73    def __le__(self, other):
74        return self.convert(other) <= other
75    def __eq__(self, other):
76        return self.convert(other) == other
77    def __ne__(self, other):
78        return self.convert(other) != other
79    def __gt__(self, other):
80        return self.convert(other) > other
81    def __ge__(self, other):
82        return self.convert(other) >= other
83
84    def __add__(self, other):
85        return self.convert(other) + other
86    def __sub__(self, other):
87        return self.convert(other) - other
88    def __mul__(self, other):
89        return self.convert(other) * other
90    def __div__(self, other):
91        return self.convert(other) / other
92    def __truediv__(self, other):
93        return self.convert(other) / other
94
95    def __radd__(self, other):
96        return other + self.convert(other)
97    def __rsub__(self, other):
98        return other - self.convert(other)
99    def __rmul__(self, other):
100        return other * self.convert(other)
101    def __rdiv__(self, other):
102        return other / self.convert(other)
103    def __rtruediv__(self, other):
104        return other / self.convert(other)
105
106class UndefinedVariable(object):
107    """Placeholder class to represent undefined variables.  Will
108    generally cause an exception whenever it is used, but evaluates to
109    zero for boolean truth testing such as in an if statement"""
110    def __nonzero__(self):
111        return False
112
113class SmartDict(attrdict):
114    """Dictionary class that holds strings, but intelligently converts
115    those strings to other types depending on their usage"""
116
117    def __getitem__(self, key):
118        """returns a Variable proxy if the values exists in the database and
119        returns an UndefinedVariable otherwise"""
120
121        if key in self:
122            return Variable(dict.get(self, key))
123        else:
124            # Note that this does *not* change the contents of the dict,
125            # so that even after we call env['foo'] we still get a
126            # meaningful answer from "'foo' in env" (which
127            # calls dict.__contains__, which we do not override).
128            return UndefinedVariable()
129
130    def __setitem__(self, key, item):
131        """intercept the setting of any variable so that we always
132        store strings in the dict"""
133        dict.__setitem__(self, key, str(item))
134
135    def values(self):
136        return [ Variable(v) for v in dict.values(self) ]
137
138    def itervalues(self):
139        for value in dict.itervalues(self):
140            yield Variable(value)
141
142    def items(self):
143        return [ (k, Variable(v)) for k,v in dict.items(self) ]
144
145    def iteritems(self):
146        for key,value in dict.iteritems(self):
147            yield key, Variable(value)
148
149    def get(self, key, default='False'):
150        return Variable(dict.get(self, key, str(default)))
151
152    def setdefault(self, key, default='False'):
153        return Variable(dict.setdefault(self, key, str(default)))
154
155__all__ = [ 'SmartDict' ]
156