smartdict.py revision 13719:74853963ddcf 
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
46import six
47if six.PY3:
48    long = int
49
50from .convert import *
51from .attrdict import attrdict
52
53class Variable(str):
54    """Intelligent proxy class for SmartDict.  Variable will use the
55    various convert functions to attempt to convert values to useable
56    types"""
57    def __int__(self):
58        return toInteger(str(self))
59    def __long__(self):
60        return toLong(str(self))
61    def __float__(self):
62        return toFloat(str(self))
63    def __bool__(self):
64        return toBool(str(self))
65    # Python 2.7 uses __nonzero__ instead of __bool__
66    __nonzero__ = __bool__
67    def convert(self, other):
68        t = type(other)
69        if t == bool:
70            return bool(self)
71        if t == int:
72            return int(self)
73        if t == long:
74            return long(self)
75        if t == float:
76            return float(self)
77        return str(self)
78    def __lt__(self, other):
79        return self.convert(other) < other
80    def __le__(self, other):
81        return self.convert(other) <= other
82    def __eq__(self, other):
83        return self.convert(other) == other
84    def __ne__(self, other):
85        return self.convert(other) != other
86    def __gt__(self, other):
87        return self.convert(other) > other
88    def __ge__(self, other):
89        return self.convert(other) >= other
90
91    def __add__(self, other):
92        return self.convert(other) + other
93    def __sub__(self, other):
94        return self.convert(other) - other
95    def __mul__(self, other):
96        return self.convert(other) * other
97    def __div__(self, other):
98        return self.convert(other) / other
99    def __truediv__(self, other):
100        return self.convert(other) / other
101
102    def __radd__(self, other):
103        return other + self.convert(other)
104    def __rsub__(self, other):
105        return other - self.convert(other)
106    def __rmul__(self, other):
107        return other * self.convert(other)
108    def __rdiv__(self, other):
109        return other / self.convert(other)
110    def __rtruediv__(self, other):
111        return other / self.convert(other)
112
113class UndefinedVariable(object):
114    """Placeholder class to represent undefined variables.  Will
115    generally cause an exception whenever it is used, but evaluates to
116    zero for boolean truth testing such as in an if statement"""
117    def __bool__(self):
118        return False
119
120    # Python 2.7 uses __nonzero__ instead of __bool__
121    __nonzero__ = __bool__
122
123class SmartDict(attrdict):
124    """Dictionary class that holds strings, but intelligently converts
125    those strings to other types depending on their usage"""
126
127    def __getitem__(self, key):
128        """returns a Variable proxy if the values exists in the database and
129        returns an UndefinedVariable otherwise"""
130
131        if key in self:
132            return Variable(dict.get(self, key))
133        else:
134            # Note that this does *not* change the contents of the dict,
135            # so that even after we call env['foo'] we still get a
136            # meaningful answer from "'foo' in env" (which
137            # calls dict.__contains__, which we do not override).
138            return UndefinedVariable()
139
140    def __setitem__(self, key, item):
141        """intercept the setting of any variable so that we always
142        store strings in the dict"""
143        dict.__setitem__(self, key, str(item))
144
145    def values(self):
146        for value in dict.values(self):
147            yield Variable(value)
148
149    def items(self):
150        for key,value in dict.items(self):
151            yield key, Variable(value)
152
153    def get(self, key, default='False'):
154        return Variable(dict.get(self, key, str(default)))
155
156    def setdefault(self, key, default='False'):
157        return Variable(dict.setdefault(self, key, str(default)))
158
159__all__ = [ 'SmartDict' ]
160