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comparison mercurial/demandload.py @ 1826:f3abe0bdccdd

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rewrite demandload module to be more flexible. performance not affected. old demandload module could only import top-level modules like os and sys. with rewrite, all of following syntax is emulated perfectly: import foo, bar foo bar import foo.bar.quux foo.bar.quux from foo.bar import quux, blurfl foo.bar:quux,blurfl only thing missing is "import foo as bar". also, namespace clashes between placeholder object and demand loaded module are no longer possible.
author Vadim Gelfer <vadim.gelger@gmail.com>
date Thu, 02 Mar 2006 11:38:03 -0800
parents 3db700146536
children d01eac5968c6
comparison
equal deleted inserted replaced
1819:d657bfdc06c4 1826:f3abe0bdccdd
1 '''Demand load modules when used, not when imported.'''
2
3 __author__ = '''Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>.
4 This software may be used and distributed according to the terms
5 of the GNU General Public License, incorporated herein by reference.'''
6
7 # this is based on matt's original demandload module. it is a
8 # complete rewrite. some time, we may need to support syntax of
9 # "import foo as bar".
10
11 class _importer(object):
12 '''import a module. it is not imported until needed, and is
13 imported at most once per scope.'''
14
15 def __init__(self, scope, modname, fromlist):
16 '''scope is context (globals() or locals()) in which import
17 should be made. modname is name of module to import.
18 fromlist is list of modules for "from foo import ..."
19 emulation.'''
20
21 self.scope = scope
22 self.modname = modname
23 self.fromlist = fromlist
24 self.mod = None
25
26 def module(self):
27 '''import the module if needed, and return.'''
28 if self.mod is None:
29 self.mod = __import__(self.modname, self.scope, self.scope,
30 self.fromlist)
31 del self.modname, self.fromlist
32 return self.mod
33
34 class _replacer(object):
35 '''placeholder for a demand loaded module. demandload puts this in
36 a target scope. when an attribute of this object is looked up,
37 this object is replaced in the target scope with the actual
38 module.
39
40 we use __getattribute__ to avoid namespace clashes between
41 placeholder object and real module.'''
42
43 def __init__(self, importer, target):
44 self.importer = importer
45 self.target = target
46 # consider case where we do this:
47 # demandload(globals(), 'foo.bar foo.quux')
48 # foo will already exist in target scope when we get to
49 # foo.quux. so we remember that we will need to demandload
50 # quux into foo's scope when we really load it.
51 self.later = []
52
53 def module(self):
54 return object.__getattribute__(self, 'importer').module()
55
56 def __getattribute__(self, key):
57 '''look up an attribute in a module and return it. replace the
58 name of the module in the caller\'s dict with the actual
59 module.'''
60
61 module = object.__getattribute__(self, 'module')()
62 target = object.__getattribute__(self, 'target')
63 importer = object.__getattribute__(self, 'importer')
64 later = object.__getattribute__(self, 'later')
65
66 if later:
67 demandload(module.__dict__, ' '.join(later))
68
69 importer.scope[target] = module
70
71 return getattr(module, key)
72
73 class _replacer_from(_replacer):
74 '''placeholder for a demand loaded module. used for "from foo
75 import ..." emulation. semantics of this are different than
76 regular import, so different implementation needed.'''
77
78 def module(self):
79 importer = object.__getattribute__(self, 'importer')
80 target = object.__getattribute__(self, 'target')
81
82 return getattr(importer.module(), target)
83
1 def demandload(scope, modules): 84 def demandload(scope, modules):
2 class d: 85 '''import modules into scope when each is first used.
3 def __getattr__(self, name):
4 mod = self.__dict__["mod"]
5 scope = self.__dict__["scope"]
6 scope[mod] = __import__(mod, scope, scope, [])
7 return getattr(scope[mod], name)
8 86
9 for m in modules.split(): 87 scope should be the value of globals() in the module calling this
10 dl = d() 88 function, or locals() in the calling function.
11 dl.mod = m
12 dl.scope = scope
13 scope[m] = dl
14 89
90 modules is a string listing module names, separated by white
91 space. names are handled like this:
15 92
93 foo import foo
94 foo bar import foo, bar
95 foo.bar import foo.bar
96 foo:bar from foo import bar
97 foo:bar,quux from foo import bar, quux
98 foo.bar:quux from foo.bar import quux'''
99
100 for mod in modules.split():
101 col = mod.find(':')
102 if col >= 0:
103 fromlist = mod[col+1:].split(',')
104 mod = mod[:col]
105 else:
106 fromlist = []
107 importer = _importer(scope, mod, fromlist)
108 if fromlist:
109 for name in fromlist:
110 scope[name] = _replacer_from(importer, name)
111 else:
112 dot = mod.find('.')
113 if dot >= 0:
114 basemod = mod[:dot]
115 val = scope.get(basemod)
116 # if base module has already been demandload()ed,
117 # remember to load this submodule into its namespace
118 # when needed.
119 if isinstance(val, _replacer):
120 later = object.__getattribute__(val, 'later')
121 later.append(mod[dot+1:])
122 continue
123 else:
124 basemod = mod
125 scope[basemod] = _replacer(importer, basemod)