在 buildbot master.cfg 文件的上下文中，如何使用本机模块基于字符串实例化 class

Question

有现货 python，我可以执行以下操作，根据包含其名称的字符串实例化 class：

#!/usr/bin/env python2.7
import sys
class Foo(object): pass
cls = getattr(sys.modules[__name__], 'Foo')
instance = cls()
print repr(instance)

输出如下：

ahammond@af6119›~⁑ ./test.py
<__main__.Foo object at 0x1095b0a10>

我想在 buildbot master.cfg 文件中做一些类似的事情，但是下面的（简化）

class BaseBuild(object): pass

class BuildStashToSrpmsToRpmsToDepot(BaseBuild):

    def init(name, build_type):
        self.name = name

    def setup():
        pass  # actually does stuff here, but...

for build_name, build_options in config['builds'].iteritems():
    cls = getattr(sys.modules[__name__], build_options['build_type'])
    build = cls(name=build_name, **build_options)
    build.setup()

生产

2015-03-11 18:39:24-0700 [-] error while parsing config file:
    Traceback (most recent call last):
      File "/opt/buildbot_virtualenv/lib/python2.7/site-packages/twisted/internet/defer.py", line 577, in _runCallbacks
        current.result = callback(current.result, *args, **kw)
      File "/opt/buildbot_virtualenv/lib/python2.7/site-    packages/twisted/internet/defer.py", line 1155, in gotResult
        _inlineCallbacks(r, g, deferred)
      File "/opt/buildbot_virtualenv/lib/python2.7/site-packages/twisted/internet/defer.py", line 1099, in _inlineCallbacks
        result = g.send(result)
      File "/opt/buildbot_git/master/buildbot/master.py", line 189, in startService
        self.configFileName)
    --- <exception caught here> ---
      File "/opt/buildbot_git/master/buildbot/config.py", line 156, in loadConfig
        exec f in localDict
      File "/home/buildbot/master.cfg", line 208, in <module>
        cls = getattr(sys.modules[__name__], build_options['build_type'])
    exceptions.AttributeError: 'module' object has no attribute 'BuildStashToSrpmsToRpmsToDepot'

2015-03-11 18:39:24-0700 [-] Configuration Errors:
2015-03-11 18:39:24-0700 [-]   error while parsing config file: 'module' object has no attribute 'BuildStashToSrpmsToRpmsToDepot' (traceback in logfile)

换句话说，我想我真正想问的是加载新 master.cfg 时使用的临时模块是什么，我如何引用它？

我目前正在使用 { 'class name': class_object } 的字典映射，但我更喜欢更原生的东西。

Answer 1

你的问题是：当运行 buildbot 时，你的 dunder 名称（__ name __ 没有空格...）当 buildbot exec 你的配置是 buildbot.config，这就是为什么 'module object has no attribute...'.

我想你可以做任何你想做的事，使 build_options 字典的值成为 class 本身，而不是具有 class 名称的字符串。像这样：

class BaseBuild(object): pass

class BuildStashToSrpmsToRpmsToDepot(BaseBuild):

    def init(name, build_type):
        self.name = name

    def setup():
        pass  # actually does stuff here, but...

# here the dict goes with key/class not key/class name
build_options = {'build_type': BuildStashToSrpmsToRpmsToDepot}

for build_name, build_options in config['builds'].iteritems():
    cls = build_options['build_type']
    build = cls(name=build_name, **build_options)
    build.setup()

以防万一，这就是 buildbot exec master.cfg（模块 buildbot.config）的方式：

# ...
# execute the config file
localDict = {
    'basedir': os.path.expanduser(basedir),
    '__file__': os.path.abspath(filename),
}

# from here on out we can batch errors together for the user's
# convenience
global _errors
_errors = errors = ConfigErrors()

old_sys_path = sys.path[:]
sys.path.append(basedir)
try:
    try:
        exec f in localDict
    except ConfigErrors, e:
        for err in e.errors:
            error(err)
        raise errors
    except:
        log.err(failure.Failure(), 'error while parsing config file:')
        error("error while parsing config file: %s (traceback in logfile)" % (sys.exc_info()[1],),)
        raise errors
finally:
    f.close()
    sys.path[:] = old_sys_path
        _errors = None
# ...

Answer 2

好的，那么问题来了：

cls = getattr(sys.modules[__name__], build_options['build_type'])

这不起作用，因为 exec 使得 __name__ 具有值 "__builtin__"。但是，您可以使用 globals() 获取当前全局变量：

cls = globals()[build_options['build_type']]

例如，如果我将以下代码添加到一个全新的 master.cfg 文件（由 buildbot create-master master 自动创建的文件，从 master.cfg.sample 重命名）：

# Load the configuration from somewhere.
import json
config = json.load(open("./config.json"))

class BaseBuild(object):
    pass

class Something(BaseBuild):

    def __init__(self, name, build_type):
        self.name = name

    def setup(self):
        print self.name, "something setup called"

class SomethingElse(BaseBuild):

    def __init__(self, name, build_type):
        self.name = name

    def setup(self):
        print self.name, "something else setup called"

for build_name, build_options in config['builds'].iteritems():
    cls = globals()[build_options['build_type']]
    build = cls(name=build_name, **build_options)
    build.setup()

然后我在与 master.cfg 相同的目录中创建以下 config.json 文件：

{
    "builds": {
        "one": {
            "build_type": "Something"
        },
        "two": {
            "build_type": "SomethingElse"
        }
    }
}

然后当我运行 buildbot start master 时，我会在日志中得到这些行：

2015-03-13 12:11:05-0400 [-] two something else setup called
2015-03-13 12:11:05-0400 [-] one something setup called

在 buildbot master.cfg 文件的上下文中，如何使用本机模块基于字符串实例化 class

In the context of a buildbot master.cfg file, how do I instantiate a class based on a string using native modules

python

introspection

twisted

buildbot