tornado中一些通用的函数和类

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本篇记录tornado源代码阅读过程中一些有意思的函数和类等，偏向于python编程技巧语法等。

ObjectDict

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class ObjectDict(dict):
    """Makes a dictionary behave like an object, with attribute-style access.
    """
    def __getattr__(self, name):
        try:
            return self[name]
        except KeyError:
            raise AttributeError(name)
    def __setattr__(self, name, value):
        self[name] = value
od = ObjectDict()
od.a = 1
od['a']		# 1
od.a		# 1

import_object

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def import_object(name):
    """Imports an object by name.
    import_object('x') is equivalent to 'import x'.
    import_object('x.y.z') is equivalent to 'from x.y import z'.
    >>> import tornado.escape
    >>> import_object('tornado.escape') is tornado.escape
    True
    >>> import_object('tornado.escape.utf8') is tornado.escape.utf8
    True
    >>> import_object('tornado') is tornado
    True
    >>> import_object('tornado.missing_module')
    Traceback (most recent call last):
        ...
    ImportError: No module named missing_module
    """
    if name.count('.') == 0:
        return __import__(name, None, None)
    parts = name.split('.')
    obj = __import__('.'.join(parts[:-1]), None, None, [parts[-1]], 0)
    try:
        return getattr(obj, parts[-1])
    except AttributeError:
        raise ImportError("No module named %s" % parts[-1])

比importlib.import_module更加方便，import_object可以直接导入模块或者属性，而前者只能导入模块。另外注意两个函数都是将导入的对象返回，而不是将其暴露在当前域名中， 和import有差距。

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import_object('os')
os	#NameError
path_exists = import_object('os.path.exists')
# from  os.path import exists as path_exists
####################
mypath = importlib.import_module('.path', 'os')
# from os import path as mypath

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