Python的import嵌套
[root@fuel ~]# vi /var/lib/docker/devicemapper/mnt/4da57a0078c9d3f32e819373b67de41da37c34a27ee03f74016427e0223df5f2/rootfs/usr/lib/python2.6/site-packages/nailgun/db/sqlalchemy/models/node.py
88
89 class Node(Base):
304 @classmethod
305 def delete_by_ids(cls, ids):
306 db.query(Node).filter(Node.id.in_(ids)).delete('fetch')
32 from nailgun.db import db
可看出引用了/usr/lib/python2.6/site-packages/nailgun/db.py中的db变量。
发现db.py不存在：
[root@fuel ~]# ls -l /var/lib/docker/devicemapper/mnt/4da57a0078c9d3f32e819373b67de41da37c34a27ee03f74016427e0223df5f2/rootfs/usr/lib/python2.6/site-packages/nailgun/db.py
进入nailgun目录：
[root@fuel ~]# cd /var/lib/docker/devicemapper/mnt/4da57a0078c9d3f32e819373b67de41da37c34a27ee03f74016427e0223df5f2/rootfs/usr/lib/python2.6/site-packages/nailgun
[root@fuel nailgun]# ls
发现nailgun目录下还有一个db目录：
[root@fuel nailgun]# cd db
[root@fuel db]# ls
deadlock_detector.py deadlock_detector.pyo __init__.pyc migration
deadlock_detector.pyc __init__.py __init__.pyo sqlalchemy
从网络了解到：“__init__.py”会在被导入时执行，因此这是Python另一种导入方式。
[root@fuel db]# vi __init__.py
17 from nailgun.db.sqlalchemy import db
可看出引用了/usr/lib/python2.6/site-packages/nailgun/db/sqlalchemy.py中的db变量。
同样不存在sqlalchemy.py，但存在sqlalchemy目录：
[root@fuel sqlalchemy]# vi __init__.py
80 db = scoped_session(
81 sessionmaker(
82 autoflush=True,
83 autocommit=False,
84 bind=engine,
85 query_cls=query_class,
86 class_=session_class
87 )
88 )
24 from sqlalchemy.orm import scoped_session
26 from sqlalchemy.orm import sessionmaker
可看出引用了/usr/lib/python2.6/site-packages/sqlalchemy/orm.py中的scoped_session、sessionmaker变量。不存在orm.py，且不存在orm目录。
19 from sqlalchemy import create_engine
31 from nailgun.db.sqlalchemy import utils
35 db_str = utils.make_dsn(**settings.DATABASE)
36 engine = create_engine(db_str, client_encoding='utf8')
可看出引用了/usr/lib/python2.6/site-packages/nailgun/db/sqlalchemy.py中的utils对象或/usr/lib/python2.6/site-packages/nailgun/db/sqlalchemy/__init__.py中引用了utils对象。
db_str明显是数据库连接字符串，内容是“postgresql://nailgun:dvbbYDuU@168.5.21.2:5432/nailgun”。
72 if settings.DEVELOPMENT:
73 query_class = DeadlockDetectingQuery
74 session_class = DeadlockDetectingSession
75 else:
76 query_class = NoCacheQuery
77 session_class = Session
32 from nailgun.settings import settings
进入docker：
[root@fuel sqlalchemy]# docker exec -it fuel-core-6.1-nailgun /bin/sh
sh-4.1# cd /usr/lib/python2.6/site-packages/nailgun/db/sqlalchemy
sh-4.1# vi __init__.py
33 #zzy added
34 from nailgun.logger import logger
35 import sys
82 #zzy added
83 logger.warning('____ffff____')
84 logger.warning(sys.path)
sh-4.1# python __init__.py
sh-4.1# tail -n 20 /tmp/nailgun.log |grep WARNING
2016-01-27 06:24:20.257 WARNING [7f92c5287700] (__init__) ____ffff____
2016-01-27 06:24:20.257 WARNING [7f92c5287700] (__init__) ['/usr/lib/python2.6/site-packages/nailgun/db/sqlalchemy', '/usr/lib64/python26.zip', '/usr/lib64/python2.6', '/usr/lib64/python2.6/plat-linux2', '/usr/lib64/python2.6/lib-tk', '/usr/lib64/python2.6/lib-old', '/usr/lib64/python2.6/lib-dynload', '/usr/lib64/python2.6/site-packages', '/usr/lib/python2.6/site-packages']
orm.py或orm目录使用以下命令查找：
ls /usr/lib/python2.6/site-packages/nailgun/db/sqlalchemy/sqlalchemy/orm*
ls /usr/lib64/python26.zip/sqlalchemy/orm*
ls /usr/lib64/python2.6/sqlalchemy/orm*
ls /usr/lib64/python2.6/plat-linux2/sqlalchemy/orm*
ls /usr/lib64/python2.6/lib-tk/sqlalchemy/orm*
ls /usr/lib64/python2.6/lib-old/sqlalchemy/orm*
ls /usr/lib64/python2.6/lib-dynload/sqlalchemy/orm*
ls /usr/lib64/python2.6/site-packages/sqlalchemy/orm*
ls /usr/lib/python2.6/site-packages/sqlalchemy/orm*
最终发现：
sh-4.1# cd /usr/lib64/python2.6/site-packages/sqlalchemy/orm
sh-4.1# vi __init__.py
63 from .scoping import (
64 scoped_session
65 )
56 from .session import (
57 Session,
58 object_session,
59 sessionmaker,
60 make_transient,
61 make_transient_to_detached
62 )
从网络了解到，“.scoping”指“__init__.py”同一级目录的“scoping.py”：
sh-4.1# vi scoping.py
14 __all__ = ['scoped_session']
15
16
17 class scoped_session(object):
18 """Provides scoped management of :class:`.Session` objects.
“__all__”定义只导出scoped_session类（当scoping.py被import的时候）。
sh-4.1# vi session.py
27 __all__ = ['Session', 'SessionTransaction',
28 'SessionExtension', 'sessionmaker']
2253 class sessionmaker(_SessionClassMethods):
2254
2255 """A configurable :class:`.Session` factory.
2256
2257 The :class:`.sessionmaker` factory generates new
2258 :class:`.Session` objects when called, creating them given
2259 the configurational arguments established here.
/usr/lib64/python2.6/site-packages/sqlalchemy/orm/scoping.py
105 def query_property(self, query_cls=None):
106 """return a class property which produces a :class:`.Query` object
107 against the class and the current :class:`.Session` when called.
108
109 e.g.::
110
111 Session = scoped_session(sessionmaker())
112
113 class MyClass(object):
114 query = Session.query_property()
115
116 # after mappers are defined
117 result = MyClass.query.filter(MyClass.name=='foo').all()
118
119 Produces instances of the session's configured query class by
120 default. To override and use a custom implementation, provide
121 a ``query_cls`` callable. The callable will be invoked with
122 the class's mapper as a positional argument and a session
123 keyword argument.
124
125 There is no limit to the number of query properties placed on
126 a class.
127
128 """
129 class query(object):
130 def __get__(s, instance, owner):
131 try:
132 mapper = class_mapper(owner)
133 if mapper:
134 if query_cls:
135 # custom query class
136 return query_cls(mapper, session=self.registry() )
137 else:
138 # session's configured query class
139 return self.registry().query(mapper)
140 except orm_exc.UnmappedClassError:
141 return None
142 return query()
143
