1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
|
"""Miscellaneous utility functions and classes.
This module is used internally by Tornado. It is not necessarily expected
that the functions and classes defined here will be useful to other
applications, but they are documented here in case they are.
The one public-facing part of this module is the `Configurable` class
and its `~Configurable.configure` method, which becomes a part of the
interface of its subclasses, including `.AsyncHTTPClient`, `.IOLoop`,
and `.Resolver`.
"""
from __future__ import absolute_import, division, print_function, with_statement
import sys
def import_object(name):
"""Imports an object by name.
import_object('x') is equivalent to 'import x'.
import_object('x.y.z') is equivalent to 'from x.y import z'.
>>> import tornado.escape
>>> import_object('tornado.escape') is tornado.escape
True
>>> import_object('tornado.escape.utf8') is tornado.escape.utf8
True
>>> import_object('tornado') is tornado
True
>>> import_object('tornado.missing_module')
Traceback (most recent call last):
...
ImportError: No module named missing_module
"""
if name.count('.') == 0:
return __import__(name, None, None)
parts = name.split('.')
obj = __import__('.'.join(parts[:-1]), None, None, [parts[-1]], 0)
try:
return getattr(obj, parts[-1])
except AttributeError:
raise ImportError("No module named %s" % parts[-1])
# Fake unicode literal support: Python 3.2 doesn't have the u'' marker for
# literal strings, and alternative solutions like "from __future__ import
# unicode_literals" have other problems (see PEP 414). u() can be applied
# to ascii strings that include \u escapes (but they must not contain
# literal non-ascii characters).
if type('') is not type(b''):
def u(s):
return s
bytes_type = bytes
unicode_type = str
basestring_type = str
else:
def u(s):
return s.decode('unicode_escape')
bytes_type = str
unicode_type = unicode
basestring_type = basestring
if sys.version_info > (3,):
exec("""
def raise_exc_info(exc_info):
raise exc_info[1].with_traceback(exc_info[2])
def exec_in(code, glob, loc=None):
if isinstance(code, str):
code = compile(code, '<string>', 'exec', dont_inherit=True)
exec(code, glob, loc)
""")
else:
exec("""
def raise_exc_info(exc_info):
raise exc_info[0], exc_info[1], exc_info[2]
def exec_in(code, glob, loc=None):
if isinstance(code, basestring):
# exec(string) inherits the caller's future imports; compile
# the string first to prevent that.
code = compile(code, '<string>', 'exec', dont_inherit=True)
exec code in glob, loc
""")
class Configurable(object):
"""Base class for configurable interfaces.
A configurable interface is an (abstract) class whose constructor
acts as a factory function for one of its implementation subclasses.
The implementation subclass as well as optional keyword arguments to
its initializer can be set globally at runtime with `configure`.
By using the constructor as the factory method, the interface
looks like a normal class, `isinstance` works as usual, etc. This
pattern is most useful when the choice of implementation is likely
to be a global decision (e.g. when `~select.epoll` is available,
always use it instead of `~select.select`), or when a
previously-monolithic class has been split into specialized
subclasses.
Configurable subclasses must define the class methods
`configurable_base` and `configurable_default`, and use the instance
method `initialize` instead of ``__init__``.
"""
__impl_class = None
__impl_kwargs = None
def __new__(cls, **kwargs):
base = cls.configurable_base()
args = {}
if cls is base:
impl = cls.configured_class()
if base.__impl_kwargs:
args.update(base.__impl_kwargs)
else:
impl = cls
args.update(kwargs)
instance = super(Configurable, cls).__new__(impl)
# initialize vs __init__ chosen for compatiblity with AsyncHTTPClient
# singleton magic. If we get rid of that we can switch to __init__
# here too.
instance.initialize(**args)
return instance
@classmethod
def configurable_base(cls):
"""Returns the base class of a configurable hierarchy.
This will normally return the class in which it is defined.
(which is *not* necessarily the same as the cls classmethod parameter).
"""
raise NotImplementedError()
@classmethod
def configurable_default(cls):
"""Returns the implementation class to be used if none is configured."""
raise NotImplementedError()
def initialize(self):
"""Initialize a `Configurable` subclass instance.
Configurable classes should use `initialize` instead of ``__init__``.
"""
@classmethod
def configure(cls, impl, **kwargs):
"""Sets the class to use when the base class is instantiated.
Keyword arguments will be saved and added to the arguments passed
to the constructor. This can be used to set global defaults for
some parameters.
"""
base = cls.configurable_base()
if isinstance(impl, (unicode_type, bytes_type)):
impl = import_object(impl)
if impl is not None and not issubclass(impl, cls):
raise ValueError("Invalid subclass of %s" % cls)
base.__impl_class = impl
base.__impl_kwargs = kwargs
@classmethod
def configured_class(cls):
"""Returns the currently configured class."""
base = cls.configurable_base()
if cls.__impl_class is None:
base.__impl_class = cls.configurable_default()
return base.__impl_class
@classmethod
def _save_configuration(cls):
base = cls.configurable_base()
return (base.__impl_class, base.__impl_kwargs)
@classmethod
def _restore_configuration(cls, saved):
base = cls.configurable_base()
base.__impl_class = saved[0]
base.__impl_kwargs = saved[1]
|
