如果模块的名称相同，为什么python会查找模块而不是包？

以下是我的目录结构：

/home/dmugtasimov/tmp/name-res
    root
        tests
            __init__.py
            test_1.py
        __init__.py
        classes.py
        extra.py
        root.py

文件内容： root/tests/_init.py

root/tests/test_1.py

root/\u init.py-空
root/classes.py

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    sys.path.insert(0, ROOT_DIRECTORY)

print 'sys.path:', sys.path
print 'BEFORE: import root.extra'
import root.extra
print 'AFTER: import root.extra'

class Class1(object):
    pass

class Class2(object):
    pass

class Class3(object):
    pass

import os
import sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    sys.path.insert(0, ROOT_DIRECTORY)
from classes import Class2

root/extra.py

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    sys.path.insert(0, ROOT_DIRECTORY)

print 'sys.path:', sys.path
print 'BEFORE: import root.extra'
import root.extra
print 'AFTER: import root.extra'

class Class1(object):
    pass

class Class2(object):
    pass

class Class3(object):
    pass

import os
import sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    sys.path.insert(0, ROOT_DIRECTORY)
from classes import Class2

root/root.py

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    sys.path.insert(0, ROOT_DIRECTORY)

print 'sys.path:', sys.path
print 'BEFORE: import root.extra'
import root.extra
print 'AFTER: import root.extra'

class Class1(object):
    pass

class Class2(object):
    pass

class Class3(object):
    pass

import os
import sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    sys.path.insert(0, ROOT_DIRECTORY)
from classes import Class2

---

我得到以下输出：

$ python -m unittest tests.test_1
sys.path: ['/home/dmugtasimov/tmp/name-res', '', '/usr/local/lib/python2.7/dist-packages/tornado-2.3-py2.7.egg', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PIL', '/usr/lib/python2.7/dist-packages/gst-0.10', '/usr/lib/python2.7/dist-packages/gtk-2.0', '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']
BEFORE: import root.extra
sys.path: ['/home/dmugtasimov/tmp/name-res', '', '/usr/local/lib/python2.7/dist-packages/tornado-2.3-py2.7.egg', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PIL', '/usr/lib/python2.7/dist-packages/gst-0.10', '/usr/lib/python2.7/dist-packages/gtk-2.0', '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']
BEFORE: import root.extra
Traceback (most recent call last):
 File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
 File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
 File "/usr/lib/python2.7/unittest/__main__.py", line 12, in <module>
    main(module=None)
 File "/usr/lib/python2.7/unittest/main.py", line 94, in __init__
    self.parseArgs(argv)
 File "/usr/lib/python2.7/unittest/main.py", line 149, in parseArgs
    self.createTests()
 File "/usr/lib/python2.7/unittest/main.py", line 158, in createTests
    self.module)
 File "/usr/lib/python2.7/unittest/loader.py", line 128, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
 File "/usr/lib/python2.7/unittest/loader.py", line 91, in loadTestsFromName
    module = __import__('.'.join(parts_copy))
 File "tests/__init__.py", line 9, in <module>
    from root.tests import test_1
 File "/home/dmugtasimov/tmp/name-res/root/tests/__init__.py", line 9, in <module>
    from root.tests import test_1
 File "/home/dmugtasimov/tmp/name-res/root/tests/test_1.py", line 3, in <module>
    from root.classes import Class1
 File "/home/dmugtasimov/tmp/name-res/root/classes.py", line 9, in <module>
    import root.extra
 File "/home/dmugtasimov/tmp/name-res/root/root.py", line 6, in <module>
    from classes import Class2
ImportError: cannot import name Class2

---

根据python文档： 导入名为spam的模块时，解释器首先搜索具有该名称的内置模块。如果未找到，则在变量sys.path给定的目录列表中搜索名为spam.py的文件

这意味着python应该查看sys.path索引0条目，获取路径“/home/dmugtasimov/tmp/name res”，找到名为root的包，然后在此包中搜索名为extra的模块。但它在/home/dmugtasimov/tmp/name res/root/目录中搜索模块根，然后尝试在其中查找名为extra的内容。发生了什么事？这与官方文件不矛盾吗？或者搜索包的规则与模块的规则不同？如果是，这些规则是否包含在文档中

更新 我把它放在这里是为了更好地格式化。

---

为了进一步调查，请执行以下操作：

删除root.pyc

将root.py重命名为root2.py

运行python-vv-m unittest tests.test_1

在最初的4次尝试中，python似乎只忽略sys.path

更新2 简化版：

/home/dmugtasimov/tmp/name-res3/xyz
    __init__.py
    a.py
    b.py
    t.py
    xyz.py

文件init.py、b.py和xyz.py为空
文件a.py：

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    print 'sys.path is modified in a.py'
    sys.path.insert(0, ROOT_DIRECTORY)
else:
    print 'sys.path is NOT modified in a.py'

print 'sys.path:', sys.path
print 'BEFORE import xyz.b'
import xyz.b
print 'AFTER import xyz.b'

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    print 'sys.path is modified in a.py'
    sys.path.insert(0, ROOT_DIRECTORY)
else:
    print 'sys.path is NOT modified in a.py'

print 'sys.path:', sys.path
print '__package__', __package__
print 'BEFORE import xyz.b'
import xyz.b
print 'AFTER import xyz.b'

文件t.py：

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    print 'sys.path is modified in t.py'
    sys.path.insert(0, ROOT_DIRECTORY)
else:
    print 'sys.path is NOT modified in t.py'

import xyz.a

运行：

输出：

运行：

输出：

运行：

输出：

输出：

但行为是不同的。对于a.py，python首先搜索包xyz，然后搜索其中的模块b：

换言之：

在目录sys.path[0]->中搜索程序包xyz

在程序包xyz中搜索模块b->找到

继续执行

对于t.py，它在与a.py自身相同的目录中搜索moduel xyz，然后在模块xyz中找不到模块b：

换言之：

在与a.py（或sys.path[1]？）相同的目录中搜索模块xyz->FOUND

在模块xyz中搜索模块b->未找到

强求恐怖

因此，看起来“import xyz.b”的用法有所不同，这取决于a.py最初作为脚本加载或从另一个模块导入的方式

更新3 我提交了文件修复方案：

更新4 更新2中描述的行为的原因现在对我来说是完全清楚的

6.4.2。包内引用

子模块通常需要相互引用。例如 环绕声模块可能使用回声模块。事实上，这些参考资料 是如此常见，以至于import语句首先在包含 在标准模块搜索路径中查找之前打包。因此 环绕声模块可以简单地使用导入回波或从回波导入 回声过滤器。如果在当前包中找不到导入的模块 （当前模块是其子模块的包），导入 语句查找具有给定名称的顶级模块

对于“python a.py”，a不被视为包中的模块，但是对于“python t.py”，a被视为包“xyz”中的模块。因此，在第一种情况下，它根据sys.path进行搜索，但在第二种情况下，它在同一个包（即“xyz”）内搜索名为“xyz”的模块（即“xyz.xyz”）

您可以很容易地看到是否像这样更改a.py：

文件a.py：

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    print 'sys.path is modified in a.py'
    sys.path.insert(0, ROOT_DIRECTORY)
else:
    print 'sys.path is NOT modified in a.py'

print 'sys.path:', sys.path
print 'BEFORE import xyz.b'
import xyz.b
print 'AFTER import xyz.b'

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    print 'sys.path is modified in a.py'
    sys.path.insert(0, ROOT_DIRECTORY)
else:
    print 'sys.path is NOT modified in a.py'

print 'sys.path:', sys.path
print '__package__', __package__
print 'BEFORE import xyz.b'
import xyz.b
print 'AFTER import xyz.b'

我的产出是：

~/tmp/name-res3/xyz$python a.py
sys.path在a.py中修改
sys.path:['/home/dmugtasimov/tmp/name-res3'，'/home/dmugtasimov/tmp/name-res3/xyz'，
“/usr/local/lib/python2.7/dist packages/tornado-2.3-py2.7.egg”，
“/usr/lib/python2.7”、“/usr/lib/python2.7/plat-linux2”，
“/usr/lib/python2.7/lib-tk”、“/usr/lib/python2.7/lib-old”，
“/usr/lib/python2.7/lib dynload”，
“/usr/local/lib/python2.7/dist包”，
“/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info”，
“/usr/lib/python2.7/dist包”，
“/usr/lib/python2.7/dist-packages/PIL”，
“/usr/lib/python2.7/dist-packages/gst-0.10”，
“/usr/lib/python2.7/dist-packages/gtk-2.0”，
“/usr/lib/python2.7/dist-packages/ubuntu-sso-client”]
__包\无
在导入xyz.b之前
导入xyz.b后
~/tmp/name-res3/xyz$python t.py
sys.path在t.py中修改
sys.path未在a.py中修改
sys.path:['/home/dmugtasimov/tmp/name-res3'，'/home/dmugtasimov/tmp/name-res3/xyz'，
“/usr/local/lib/python2.7/dist packages/tornado-2.3-py2.7.egg”，
“/usr/lib/python2.7”、“/usr/lib/python2.7/plat-linux2”，
“/usr/lib/python2.7/lib-tk”、“/usr/lib/python2.7/lib-old”，
“/usr/lib/python2.7/lib dynload”，
“/usr/local/lib/python2.7/dist包”，
“/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info”，
“/usr/lib/python2.7/dist包”，
“/usr/lib/python2.7/dist-packages/PIL”，
“/usr/lib/python2.7/dist-packages/gst-0.10”，
“/usr/lib/python2.7/dist-packages/gtk-2.0”，
“/usr/lib/python2.7/dist-packages/ubuntu-sso-client”]
__包_xyz
在导入xyz.b之前
回溯（最近一次呼叫最后一次）：
文件“t.py”，第9行，在
导入xyz.a
文件“/home/dmugtasimov/tmp/name-res3/xyz/a.py”，第12行，在
导入xyz.b
ImportError:没有名为b的模块

感谢@J.F.Sebastian指出了正确的文档位置

更新5

---

似乎还有另一个问题。如果有兴趣，请按照此处的注释进行操作：

请勿修改

sys.path

当同一模块以不同名称提供时，会导致问题。看

在代码中使用绝对或显式相对导入，并从项目目录运行脚本。使用全名运行测试：

$ python -munittest root.tests.test_1

某些软件包在内部修改系统路径，例如。，

python -vv t.py

import xyz # directory /home/dmugtasimov/tmp/name-res3/xyz
# trying /home/dmugtasimov/tmp/name-res3/xyz/__init__.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/__init__module.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/__init__.py
# /home/dmugtasimov/tmp/name-res3/xyz/__init__.pyc matches /home/dmugtasimov/tmp/name-res3/xyz/__init__.py
import xyz # precompiled from /home/dmugtasimov/tmp/name-res3/xyz/__init__.pyc
# trying /home/dmugtasimov/tmp/name-res3/xyz/a.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/amodule.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/a.py
# /home/dmugtasimov/tmp/name-res3/xyz/a.pyc matches /home/dmugtasimov/tmp/name-res3/xyz/a.py
import xyz.a # precompiled from /home/dmugtasimov/tmp/name-res3/xyz/a.pyc
# trying /home/dmugtasimov/tmp/name-res3/xyz/os.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/osmodule.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/os.py
# trying /home/dmugtasimov/tmp/name-res3/xyz/os.pyc
# trying /home/dmugtasimov/tmp/name-res3/xyz/sys.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/sysmodule.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/sys.py
# trying /home/dmugtasimov/tmp/name-res3/xyz/sys.pyc
# trying /home/dmugtasimov/tmp/name-res3/xyz/xyz.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/xyzmodule.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/xyz.py
# /home/dmugtasimov/tmp/name-res3/xyz/xyz.pyc matches /home/dmugtasimov/tmp/name-res3/xyz/xyz.py
import xyz.xyz # precompiled from /home/dmugtasimov/tmp/name-res3/xyz/xyz.pyc
#   clear[2] __file__
#   clear[2] __package__
#   clear[2] sys
#   clear[2] ROOT_DIRECTORY
#   clear[2] __name__
#   clear[2] os
sys.path is modified in t.py
sys.path is NOT modified in a.py
sys.path: ['/home/dmugtasimov/tmp/name-res3', '/home/dmugtasimov/tmp/name-res3/xyz',
 '/usr/local/lib/python2.7/dist-packages/tornado-2.3-py2.7.egg',
 '/home/dmugtasimov/tmp/name-res3/xyz', '/usr/lib/python2.7',
 '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk',
 '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload',
 '/usr/local/lib/python2.7/dist-packages',
 '/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info',
 '/usr/lib/python2.7/dist-packages',
 '/usr/lib/python2.7/dist-packages/PIL',
 '/usr/lib/python2.7/dist-packages/gst-0.10',
 '/usr/lib/python2.7/dist-packages/gtk-2.0',
 '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']
BEFORE import xyz.b
Traceback (most recent call last):
  File "t.py", line 9, in <module>
    import xyz.a
  File "/home/dmugtasimov/tmp/name-res3/xyz/a.py", line 11, in <module>
    import xyz.b
ImportError: No module named b

sys.path: ['/home/dmugtasimov/tmp/name-res3', '/home/dmugtasimov/tmp/name-res3/xyz', '/usr/local/lib/python2.7/dist-packages/tornado-2.3-py2.7.egg', '/home/dmugtasimov/tmp/name-res3/xyz', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PIL', '/usr/lib/python2.7/dist-packages/gst-0.10', '/usr/lib/python2.7/dist-packages/gtk-2.0', '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']

import xyz # directory /home/dmugtasimov/tmp/name-res3/xyz
# trying /home/dmugtasimov/tmp/name-res3/xyz/__init__.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/__init__module.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/__init__.py
# /home/dmugtasimov/tmp/name-res3/xyz/__init__.pyc matches /home/dmugtasimov/tmp/name-res3/xyz/__init__.py
import xyz # precompiled from /home/dmugtasimov/tmp/name-res3/xyz/__init__.pyc
# trying /home/dmugtasimov/tmp/name-res3/xyz/b.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/bmodule.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/b.py
# /home/dmugtasimov/tmp/name-res3/xyz/b.pyc matches /home/dmugtasimov/tmp/name-res3/xyz/b.py
import xyz.b # precompiled from /home/dmugtasimov/tmp/name-res3/xyz/b.pyc

# trying /home/dmugtasimov/tmp/name-res3/xyz/xyz.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/xyzmodule.so
# trying /home/dmugtasimov/tmp/name-res3/xyz/xyz.py
# /home/dmugtasimov/tmp/name-res3/xyz/xyz.pyc matches /home/dmugtasimov/tmp/name-res3/xyz/xyz.py
import xyz.xyz # precompiled from /home/dmugtasimov/tmp/name-res3/xyz/xyz.pyc

import os, sys
ROOT_DIRECTORY = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
if not sys.path or ROOT_DIRECTORY not in sys.path:
    print 'sys.path is modified in a.py'
    sys.path.insert(0, ROOT_DIRECTORY)
else:
    print 'sys.path is NOT modified in a.py'

print 'sys.path:', sys.path
print '__package__', __package__
print 'BEFORE import xyz.b'
import xyz.b
print 'AFTER import xyz.b'

~/tmp/name-res3/xyz $ python a.py
sys.path is modified in a.py
sys.path: ['/home/dmugtasimov/tmp/name-res3', '/home/dmugtasimov/tmp/name-res3/xyz',
 '/usr/local/lib/python2.7/dist-packages/tornado-2.3-py2.7.egg',
 '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2',
 '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old',
 '/usr/lib/python2.7/lib-dynload',
 '/usr/local/lib/python2.7/dist-packages',
 '/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info',
 '/usr/lib/python2.7/dist-packages',
 '/usr/lib/python2.7/dist-packages/PIL',
 '/usr/lib/python2.7/dist-packages/gst-0.10',
 '/usr/lib/python2.7/dist-packages/gtk-2.0',
 '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']
__package__ None
BEFORE import xyz.b
AFTER import xyz.b
~/tmp/name-res3/xyz $ python t.py
sys.path is modified in t.py
sys.path is NOT modified in a.py
sys.path: ['/home/dmugtasimov/tmp/name-res3', '/home/dmugtasimov/tmp/name-res3/xyz',
 '/usr/local/lib/python2.7/dist-packages/tornado-2.3-py2.7.egg',
 '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2',
 '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old',
 '/usr/lib/python2.7/lib-dynload',
 '/usr/local/lib/python2.7/dist-packages',
 '/usr/local/lib/python2.7/dist-packages/setuptools-0.6c11-py2.7.egg-info',
 '/usr/lib/python2.7/dist-packages',
 '/usr/lib/python2.7/dist-packages/PIL',
 '/usr/lib/python2.7/dist-packages/gst-0.10',
 '/usr/lib/python2.7/dist-packages/gtk-2.0',
 '/usr/lib/python2.7/dist-packages/ubuntu-sso-client']
__package__ xyz
BEFORE import xyz.b
Traceback (most recent call last):
  File "t.py", line 9, in <module>
    import xyz.a
  File "/home/dmugtasimov/tmp/name-res3/xyz/a.py", line 12, in <module>
    import xyz.b
ImportError: No module named b

$ python -munittest root.tests.test_1

import sys
print('sys.path = %s' % sys.path) # see that the parent of "xyz" is on sys.path
print("importing xyz.tests")
import xyz.a

# solution A: absolute_import by __future__  (or use Python 3)
#from __future__ import absolute_import
print("importing xyz.a")
# solution B: explicit relative import
#from . import b    # and remove "import xyz.b"
# solution C: relative import (not recommended)
#import b           # and remove "import xyz.b"
import xyz.b

parent_of_xyz=...  # The parent directory of "xyz" - absolute path
cd $parent_of_xyz
python -m xyz.tests.t
PYTHONPATH=$parent_of_xyz/xyz python -m unittest tests
PYTHONPATH=$parent_of_xyz     python xyz/tests/t.py

Imported xyz.xyz  !!!
...
ImportError...