Question

我在尝试将同情表达式转储到YAML时遇到此错误：

TypeError: cannot determine truth value of Relational

我想要转储的是一个包含2个sympy.Symbol个对象的集合。我不确定为什么同情会尝试将其评估为StrictLessThan对象。 sympy试图确定真值，或许是为了评估mapping.sort()函数？

这是追溯：

Traceback (most recent call last):
  File "E:/Matt/Documents/ProgrammingProjects/infinitree/abg.py", line 267, in <module>
    print yaml.dump(mtree)
  File "C:\Python27\lib\site-packages\yaml\__init__.py", line 202, in dump
    return dump_all([data], stream, Dumper=Dumper, **kwds)
  File "C:\Python27\lib\site-packages\yaml\__init__.py", line 190, in dump_all
    dumper.represent(data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 28, in represent
    node = self.represent_data(data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 61, in represent_data
    node = self.yaml_multi_representers[data_type](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 434, in represent_object
    u'tag:yaml.org,2002:python/object:'+function_name, state)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 61, in represent_data
    node = self.yaml_multi_representers[data_type](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 434, in represent_object
    u'tag:yaml.org,2002:python/object:'+function_name, state)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 57, in represent_data
    node = self.yaml_representers[data_types[0]](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 223, in represent_dict
    return self.represent_mapping(u'tag:yaml.org,2002:map', data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 61, in represent_data
    node = self.yaml_multi_representers[data_type](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 434, in represent_object
    u'tag:yaml.org,2002:python/object:'+function_name, state)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 61, in represent_data
    node = self.yaml_multi_representers[data_type](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 434, in represent_object
    u'tag:yaml.org,2002:python/object:'+function_name, state)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 57, in represent_data
    node = self.yaml_representers[data_types[0]](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 223, in represent_dict
    return self.represent_mapping(u'tag:yaml.org,2002:map', data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 57, in represent_data
    node = self.yaml_representers[data_types[0]](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 223, in represent_dict
    return self.represent_mapping(u'tag:yaml.org,2002:map', data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 61, in represent_data
    node = self.yaml_multi_representers[data_type](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 434, in represent_object
    u'tag:yaml.org,2002:python/object:'+function_name, state)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 57, in represent_data
    node = self.yaml_representers[data_types[0]](self, data)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 229, in represent_set
    return self.represent_mapping(u'tag:yaml.org,2002:set', value)
  File "C:\Python27\lib\site-packages\yaml\representer.py", line 120, in represent_mapping
    mapping.sort()
  File "C:\Python27\lib\site-packages\sympy\core\relational.py", line 195, in __nonzero__
    raise TypeError("cannot determine truth value of Relational")
TypeError: cannot determine truth value of Relational

Answer 1

表示器尝试按照与dict类似的方式对集合进行排序，方法是按键值对对项目进行排序，然后转储它们。我不知道sympy的细节，但是对于排序，需要知道密钥和值的表示（对于一个集合，只使用密钥），并且通常使用字符串表示来完成，我猜，导致评价。因此mapping.sort()会评估它用作密钥的sympy个对象，而不是相反（正如您在问题中所指出的那样）

然而，不仅仅是排序问题，sympy对象在没有其他代表程序的情况下也无法转储：

import sys
import ruamel.yaml
from sympy.abc import x, y
from  sympy.core.relational import Relational

data = Relational(y, x+x**2, '==')

ruamel.yaml.round_trip_dump(data, sys.stdout)

还有哪些错误：

ruamel.yaml.representer.RepresenterError: cannot represent an object: Eq(y, x**2 + x)

所以我开始很简单，通过为你使用的对象类型制作代表，并且想要转储，然后那些的集合也应该是可转储的。

_{我使用了ruamel.yaml库而不是仅支持YAML 1.1规范的过时的PyYAML。对于这个问题，两者都应该采用相同的方式。}

Sympy TypeError：转储到YAML

1 个答案: