tornado架构分析2 options.py实现原理

总结体会：

options这个文件是用来管理程序运行过程中配置的，它采用了单例模式，整个程序运行时只有一个实例存在。

参数可以从命令行读取，也可以从配置文件中读取，就看你怎么用了。

同时，options这个类也被tornado自己所用，存放了一些运行时的所需的参数（我只看了log.py文件，日志的一些参数的确用了options）。

实现原理：

options单例化的对象时OptionParser，OptionParser的组成：

1 一个名叫_options名称的字典对象，其中每个对象的内容都是_Option实例对象。

2 _parse_callbacks名称的列表对象，目前从定义上讲应该是回调函数的列表。

然后接着说_Option类，它实际是定义了一种数据对象格式，包括name,type,help,metavar,multiple,file_name,group_name,callback,default,_value，这些变量是作者认为在使用时可能需要定义的。

代码分段：

经过上面分析，我个人认为应该把options.py代码分为以下几段（除去了文件头import部分）：

1 类OptionParser：options存储对象的类

2 类_Mockable：这其实是作者针对依赖库变化打的补丁，我们暂时不需要考虑

class _Mockable(object):
    """`mock.patch` compatible wrapper for `OptionParser`.

    As of ``mock`` version 1.0.1, when an object uses ``__getattr__``
    hooks instead of ``__dict__``, ``patch.__exit__`` tries to delete
    the attribute it set instead of setting a new one (assuming that
    the object does not catpure ``__setattr__``, so the patch
    created a new attribute in ``__dict__``).

    _Mockable's getattr and setattr pass through to the underlying
    OptionParser, and delattr undoes the effect of a previous setattr.
    """
    def __init__(self, options):
        # Modify __dict__ directly to bypass __setattr__
        self.__dict__['_options'] = options
        self.__dict__['_originals'] = {}

    def __getattr__(self, name):
        return getattr(self._options, name)

    def __setattr__(self, name, value):
        assert name not in self._originals, "don't reuse mockable objects"
        self._originals[name] = getattr(self._options, name)
        setattr(self._options, name, value)

    def __delattr__(self, name):
        setattr(self._options, name, self._originals.pop(name))

3 类_Option：用于OptionParse的需求对象

4 options = OptionParser() ：实例化OptionParse对象

options = OptionParser()
"""Global options object.

All defined options are available as attributes on this object.
"""

5 接口区：用于对配置对象options做操作，这里的诸多函数实际上是对options对象内部函数的一个封装。注意：实例化在这里有意义了，它们是对4步options对象直接做操作，而不是对类做操作

def define(name, default=None, type=None, help=None, metavar=None,
           multiple=False, group=None, callback=None):
    """Defines an option in the global namespace.

    See `OptionParser.define`.
    """
    return options.define(name, default=default, type=type, help=help,
                          metavar=metavar, multiple=multiple, group=group,
                          callback=callback)


def parse_command_line(args=None, final=True):
    """Parses global options from the command line.

    See `OptionParser.parse_command_line`.
    """
    return options.parse_command_line(args, final=final)


def parse_config_file(path, final=True):
    """Parses global options from a config file.

    See `OptionParser.parse_config_file`.
    """
    return options.parse_config_file(path, final=final)


def print_help(file=None):
    """Prints all the command line options to stderr (or another file).

    See `OptionParser.print_help`.
    """
    return options.print_help(file)


def add_parse_callback(callback):
    """Adds a parse callback, to be invoked when option parsing is done.

    See `OptionParser.add_parse_callback`
    """
    options.add_parse_callback(callback)

6 调用函数define_logging_options(options)：这里就是tornado自己的默认运行参数了，主要是日志。指向log.py里面的一些预先设置好的配置

# Default options
define_logging_options(options)

我们跳到log.py看函数是怎么写的

def define_logging_options(options=None):
    """Add logging-related flags to ``options``.

    These options are present automatically on the default options instance;
    this method is only necessary if you have created your own `.OptionParser`.

    .. versionadded:: 4.2
        This function existed in prior versions but was broken and undocumented until 4.2.
    """
    if options is None:
        # late import to prevent cycle
        import tornado.options
        options = tornado.options.options
    options.define("logging", default="info",
                   help=("Set the Python log level. If 'none', tornado won't touch the "
                         "logging configuration."),
                   metavar="debug|info|warning|error|none")
    options.define("log_to_stderr", type=bool, default=None,
                   help=("Send log output to stderr (colorized if possible). "
                         "By default use stderr if --log_file_prefix is not set and "
                         "no other logging is configured."))
    options.define("log_file_prefix", type=str, default=None, metavar="PATH",
                   help=("Path prefix for log files. "
                         "Note that if you are running multiple tornado processes, "
                         "log_file_prefix must be different for each of them (e.g. "
                         "include the port number)"))
    options.define("log_file_max_size", type=int, default=100 * 1000 * 1000,
                   help="max size of log files before rollover")
    options.define("log_file_num_backups", type=int, default=10,
                   help="number of log files to keep")

    options.define("log_rotate_when", type=str, default='midnight',
                   help=("specify the type of TimedRotatingFileHandler interval "
                         "other options:('S', 'M', 'H', 'D', 'W0'-'W6')"))
    options.define("log_rotate_interval", type=int, default=1,
                   help="The interval value of timed rotating")

    options.define("log_rotate_mode", type=str, default='size',
                   help="The mode of rotating files(time or size)")

    options.add_parse_callback(lambda: enable_pretty_logging(options))

类OptionParser和类_Option我将在下一步单独说明

本文部分内容借鉴了：

http://blog.csdn.net/wgw335363240/article/details/50755782