smartdict.py revision 13714:35636064b7a1 
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
44from __future__ import print_function
45from __future__ import absolute_import
46
47from .convert import *
48from .attrdict import attrdict
49
50class Variable(str):
51    """Intelligent proxy class for SmartDict.  Variable will use the
52    various convert functions to attempt to convert values to useable
53    types"""
54    def __int__(self):
55        return toInteger(str(self))
56    def __long__(self):
57        return toLong(str(self))
58    def __float__(self):
59        return toFloat(str(self))
60    def __bool__(self):
61        return toBool(str(self))
62    # Python 2.7 uses __nonzero__ instead of __bool__
63    __nonzero__ = __bool__
64    def convert(self, other):
65        t = type(other)
66        if t == bool:
67            return bool(self)
68        if t == int:
69            return int(self)
70        if t == long:
71            return long(self)
72        if t == float:
73            return float(self)
74        return str(self)
75    def __lt__(self, other):
76        return self.convert(other) < other
77    def __le__(self, other):
78        return self.convert(other) <= other
79    def __eq__(self, other):
80        return self.convert(other) == other
81    def __ne__(self, other):
82        return self.convert(other) != other
83    def __gt__(self, other):
84        return self.convert(other) > other
85    def __ge__(self, other):
86        return self.convert(other) >= other
87
88    def __add__(self, other):
89        return self.convert(other) + other
90    def __sub__(self, other):
91        return self.convert(other) - other
92    def __mul__(self, other):
93        return self.convert(other) * other
94    def __div__(self, other):
95        return self.convert(other) / other
96    def __truediv__(self, other):
97        return self.convert(other) / other
98
99    def __radd__(self, other):
100        return other + self.convert(other)
101    def __rsub__(self, other):
102        return other - self.convert(other)
103    def __rmul__(self, other):
104        return other * self.convert(other)
105    def __rdiv__(self, other):
106        return other / self.convert(other)
107    def __rtruediv__(self, other):
108        return other / self.convert(other)
109
110class UndefinedVariable(object):
111    """Placeholder class to represent undefined variables.  Will
112    generally cause an exception whenever it is used, but evaluates to
113    zero for boolean truth testing such as in an if statement"""
114    def __bool__(self):
115        return False
116
117    # Python 2.7 uses __nonzero__ instead of __bool__
118    __nonzero__ = __bool__
119
120class SmartDict(attrdict):
121    """Dictionary class that holds strings, but intelligently converts
122    those strings to other types depending on their usage"""
123
124    def __getitem__(self, key):
125        """returns a Variable proxy if the values exists in the database and
126        returns an UndefinedVariable otherwise"""
127
128        if key in self:
129            return Variable(dict.get(self, key))
130        else:
131            # Note that this does *not* change the contents of the dict,
132            # so that even after we call env['foo'] we still get a
133            # meaningful answer from "'foo' in env" (which
134            # calls dict.__contains__, which we do not override).
135            return UndefinedVariable()
136
137    def __setitem__(self, key, item):
138        """intercept the setting of any variable so that we always
139        store strings in the dict"""
140        dict.__setitem__(self, key, str(item))
141
142    def values(self):
143        for value in dict.values(self):
144            yield Variable(value)
145
146    def items(self):
147        for key,value in dict.items(self):
148            yield key, Variable(value)
149
150    def get(self, key, default='False'):
151        return Variable(dict.get(self, key, str(default)))
152
153    def setdefault(self, key, default='False'):
154        return Variable(dict.setdefault(self, key, str(default)))
155
156__all__ = [ 'SmartDict' ]
157