smartdict.py revision 2665 
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 *
46
47class Variable(str):
48    """Intelligent proxy class for SmartDict.  Variable will use the
49    various convert functions to attempt to convert values to useable
50    types"""
51    def __int__(self):
52        return toInteger(str(self))
53    def __long__(self):
54        return toLong(str(self))
55    def __float__(self):
56        return toFloat(str(self))
57    def __nonzero__(self):
58        return toBool(str(self))
59    def convert(self, other):
60        t = type(other)
61        if t == bool:
62            return bool(self)
63        if t == int:
64            return int(self)
65        if t == long:
66            return long(self)
67        if t == float:
68            return float(self)
69        return str(self)
70    def __lt__(self, other):
71        return self.convert(other) < other
72    def __le__(self, other):
73        return self.convert(other) <= other
74    def __eq__(self, other):
75        return self.convert(other) == other
76    def __ne__(self, other):
77        return self.convert(other) != other
78    def __gt__(self, other):
79        return self.convert(other) > other
80    def __ge__(self, other):
81        return self.convert(other) >= other
82
83    def __add__(self, other):
84        return self.convert(other) + other
85    def __sub__(self, other):
86        return self.convert(other) - other
87    def __mul__(self, other):
88        return self.convert(other) * other
89    def __div__(self, other):
90        return self.convert(other) / other
91    def __truediv__(self, other):
92        return self.convert(other) / other
93
94    def __radd__(self, other):
95        return other + self.convert(other)
96    def __rsub__(self, other):
97        return other - self.convert(other)
98    def __rmul__(self, other):
99        return other * self.convert(other)
100    def __rdiv__(self, other):
101        return other / self.convert(other)
102    def __rtruediv__(self, other):
103        return other / self.convert(other)
104
105class UndefinedVariable(object):
106    """Placeholder class to represent undefined variables.  Will
107    generally cause an exception whenever it is used, but evaluates to
108    zero for boolean truth testing such as in an if statement"""
109    def __nonzero__(self):
110        return False
111
112class SmartDict(dict):
113    """Dictionary class that holds strings, but intelligently converts
114    those strings to other types depending on their usage"""
115
116    def __getitem__(self, key):
117        """returns a Variable proxy if the values exists in the database and
118        returns an UndefinedVariable otherwise"""
119
120        if key in self:
121            return Variable(dict.get(self, key))
122        else:
123            # Note that this does *not* change the contents of the dict,
124            # so that even after we call env['foo'] we still get a
125            # meaningful answer from "'foo' in env" (which
126            # calls dict.__contains__, which we do not override).
127            return UndefinedVariable()
128
129    def __setitem__(self, key, item):
130        """intercept the setting of any variable so that we always
131        store strings in the dict"""
132        dict.__setitem__(self, key, str(item))
133
134    def values(self):
135        return [ Variable(v) for v in dict.values(self) ]
136
137    def itervalues(self):
138        for value in dict.itervalues(self):
139            yield Variable(value)
140
141    def items(self):
142        return [ (k, Variable(v)) for k,v in dict.items(self) ]
143
144    def iteritems(self):
145        for key,value in dict.iteritems(self):
146            yield key, Variable(value)
147
148    def get(self, key, default='False'):
149        return Variable(dict.get(self, key, str(default)))
150
151    def setdefault(self, key, default='False'):
152        return Variable(dict.setdefault(self, key, str(default)))
153
154__all__ = [ 'SmartDict' ]
155