如何使用 pyYAML 将 python 元组添加到 YAML 文件？

Question

标题是不言自明的。

当我将元组保存到 YAML 文件时，我得到如下所示的内容：

ambient:  !!python/tuple [0.3, 0.3 ,0.3]

当我尝试使用 yaml.safe_load(file_object) 加载它时，我不断收到错误消息：

yaml.constructor.ConstructorError:  could not determine a constructor for the tag 'tag:yaml.org,2002:python/tuple'

需要做什么？

Answer 1

在 pyyaml 中，SafeLoader 不包含用于 python 原生类型的加载器，仅包含 yaml 规范中定义的类型。您可以在下面的交互示例中查看SafeLoader 和Loader 的类型。

你可以定义一个新的 Loader 类，添加到 python 元组中，但不能添加其他类型，所以它应该仍然很安全：

import yaml

class PrettySafeLoader(yaml.SafeLoader):
    def construct_python_tuple(self, node):
        return tuple(self.construct_sequence(node))

PrettySafeLoader.add_constructor(
    u'tag:yaml.org,2002:python/tuple',
    PrettySafeLoader.construct_python_tuple)

doc = yaml.dump(tuple("foo bar baaz".split()))
print repr(doc)
thing = yaml.load(doc, Loader=PrettySafeLoader)
print thing

导致：

'!!python/tuple [foo, bar, baaz]\n'
('foo', 'bar', 'baaz')

有关与 SafeLoader 和 Loader 类关联的构造函数，请参见下文。

>>> yaml.SafeLoader.yaml_constructors
{None: <unbound method SafeConstructor.construct_undefined>,
 u'tag:yaml.org,2002:binary': <unbound method SafeConstructor.construct_yaml_binary>,
 u'tag:yaml.org,2002:bool': <unbound method SafeConstructor.construct_yaml_bool>,
 u'tag:yaml.org,2002:float': <unbound method SafeConstructor.construct_yaml_float>,
 u'tag:yaml.org,2002:int': <unbound method SafeConstructor.construct_yaml_int>,
 u'tag:yaml.org,2002:map': <unbound method SafeConstructor.construct_yaml_map>,
 u'tag:yaml.org,2002:null': <unbound method SafeConstructor.construct_yaml_null>,
 u'tag:yaml.org,2002:omap': <unbound method SafeConstructor.construct_yaml_omap>,
 u'tag:yaml.org,2002:pairs': <unbound method SafeConstructor.construct_yaml_pairs>,
 u'tag:yaml.org,2002:seq': <unbound method SafeConstructor.construct_yaml_seq>,
 u'tag:yaml.org,2002:set': <unbound method SafeConstructor.construct_yaml_set>,
 u'tag:yaml.org,2002:str': <unbound method SafeConstructor.construct_yaml_str>,
 u'tag:yaml.org,2002:timestamp': <unbound method SafeConstructor.construct_yaml_timestamp>}

>>> yaml.Loader.yaml_constructors
{None: <unbound method SafeConstructor.construct_undefined>,
 u'tag:yaml.org,2002:binary': <unbound method SafeConstructor.construct_yaml_binary>,
 u'tag:yaml.org,2002:bool': <unbound method SafeConstructor.construct_yaml_bool>,
 u'tag:yaml.org,2002:float': <unbound method SafeConstructor.construct_yaml_float>,
 u'tag:yaml.org,2002:int': <unbound method SafeConstructor.construct_yaml_int>,
 u'tag:yaml.org,2002:map': <unbound method SafeConstructor.construct_yaml_map>,
 u'tag:yaml.org,2002:null': <unbound method SafeConstructor.construct_yaml_null>,
 u'tag:yaml.org,2002:omap': <unbound method SafeConstructor.construct_yaml_omap>,
 u'tag:yaml.org,2002:pairs': <unbound method SafeConstructor.construct_yaml_pairs>,
 u'tag:yaml.org,2002:python/bool': <unbound method Constructor.construct_yaml_bool>,
 u'tag:yaml.org,2002:python/complex': <unbound method Constructor.construct_python_complex>,
 u'tag:yaml.org,2002:python/dict': <unbound method Constructor.construct_yaml_map>,
 u'tag:yaml.org,2002:python/float': <unbound method Constructor.construct_yaml_float>,
 u'tag:yaml.org,2002:python/int': <unbound method Constructor.construct_yaml_int>,
 u'tag:yaml.org,2002:python/list': <unbound method Constructor.construct_yaml_seq>,
 u'tag:yaml.org,2002:python/long': <unbound method Constructor.construct_python_long>,
 u'tag:yaml.org,2002:python/none': <unbound method Constructor.construct_yaml_null>,
 u'tag:yaml.org,2002:python/str': <unbound method Constructor.construct_python_str>,
 u'tag:yaml.org,2002:python/tuple': <unbound method Constructor.construct_python_tuple>,
 u'tag:yaml.org,2002:python/unicode': <unbound method Constructor.construct_python_unicode>,
 u'tag:yaml.org,2002:seq': <unbound method SafeConstructor.construct_yaml_seq>,
 u'tag:yaml.org,2002:set': <unbound method SafeConstructor.construct_yaml_set>,
 u'tag:yaml.org,2002:str': <unbound method SafeConstructor.construct_yaml_str>,
 u'tag:yaml.org,2002:timestamp': <unbound method SafeConstructor.construct_yaml_timestamp>}

Answer 2

至少按照the PyYAML documentation：

yaml.safe_load 函数将这种能力限制为简单的 Python 对象，如整数或列表。

as you can see in the source 列表更广泛，但不包括 tag:yaml.org,2002:python/tuple。

看来，如果您在 YAML 文件中生成 !!python/tuple 类型，则您使用的是 dump()，而不是 safe_dump()。如果是这种情况，您可能应该改用load() 代替safe_load()，因为dump() 创建的文件不能保证safe_load() 可以加载。 （见description of safe_dump()）。

Answer 3

对于那些正在寻找最新答案的人。

目前，这个问题可以通过yaml.FullLoader解决。

import yaml
yaml_file = open("path/to/filename.yaml", 'r')
loaded_yaml = yaml.load(yaml_file, Loader=yaml.FullLoader)

然后标记为如下元组的条目将被正确解析而没有任何问题。

!!python/tuple [0.3, 0.3 ,0.3]