Question

我想优雅地通知用户他们的混乱YAML文件存在缺陷。 python-3.4.1/lib/python-3.4/yaml/scanner.py的第288行报告了一个常见的解析错误，并通过抛出异常来处理它：

raise ScannerError("while scanning a simple key", key.mark,
                   "could not found expected ':'", self.get_mark())

我正在努力报道它。

try:
    parsed_yaml = yaml.safe_load(txt)

except yaml.YAMLError as exc:
    print ("scanner error 1")
    if hasattr(exc, 'problem_mark'):
        mark = exc.problem_mark
        print("Error parsing Yaml file at line %s, column %s." %
                                            (mark.line, mark.column+1))
    else:
        print ("Something went wrong while parsing yaml file")
    return

这给出了

$ yaml_parse.py
scanner error 1
Error parsing Yaml file line 1508, column 9.

但是如何获取错误文本以及key.mark和另一个标记中的内容？

更有用的是，我如何检查PyYaml源来解决这个问题？ ScannerError类似乎忽略了参数（来自scanner.py第32行）：

class ScannerError(MarkedYAMLError):
     pass

Answer 1

根据@ Anthon的回答，这段代码效果很好：

try:
    import yaml
except:
    print ('Fatal error:  Yaml library not available')
    quit()

f = open ('y.yml')
txt = f.read()

try:
    yml = yaml.load(txt, yaml.SafeLoader)

except yaml.YAMLError as exc:
    print ("Error while parsing YAML file:")
    if hasattr(exc, 'problem_mark'):
        if exc.context != None:
            print ('  parser says\n' + str(exc.problem_mark) + '\n  ' +
                str(exc.problem) + ' ' + str(exc.context) +
                '\nPlease correct data and retry.')
        else:
            print ('  parser says\n' + str(exc.problem_mark) + '\n  ' +
                str(exc.problem) + '\nPlease correct data and retry.')
    else:
        print ("Something went wrong while parsing yaml file")
    return

# make use of `yml`

带有轻度破坏数据的示例输出：

$ yaml_parse.py
Error while parsing YAML file:
  parser says
  in "<unicode string>", line 1525, column 9:
      - name: Curve 1
            ^
  could not found expected ':' while scanning a simple key
Please correct data and retry.

$ yaml_parse.py
Error while parsing YAML file:
  parser says
  in "<unicode string>", line 1526, column 10:
        curve: title 1
             ^
  mapping values are not allowed here
Please correct data and retry.

Answer 2

ScannerError类没有定义方法（pass语句的工作方式与无操作类似。这使得它的功能与基类MarkedYAMLError相同，这就是一个谁存储数据。来自error.py：

class MarkedYAMLError(YAMLError):
    def __init__(self, context=None, context_mark=None,
                 problem=None, problem_mark=None, note=None):
        self.context = context
        self.context_mark = context_mark
        self.problem = problem
        self.problem_mark = problem_mark
        self.note = note

    def __str__(self):
        lines = []
        if self.context is not None:
            lines.append(self.context)
        if self.context_mark is not None  \
           and (self.problem is None or self.problem_mark is None
                or self.context_mark.name != self.problem_mark.name
                or self.context_mark.line != self.problem_mark.line
                or self.context_mark.column != self.problem_mark.column):
            lines.append(str(self.context_mark))
        if self.problem is not None:
            lines.append(self.problem)
        if self.problem_mark is not None:
            lines.append(str(self.problem_mark))
        if self.note is not None:
            lines.append(self.note)
        return '\n'.join(lines)

如果您从文件txt.yaml开始：

hallo: 1
bye

和test.py：

import ruamel.yaml as yaml
txt = open('txt.yaml')
data = yaml.load(txt, yaml.SafeLoader)

你会得到不那么描述性的错误：

...
ruamel.yaml.scanner.ScannerError: while scanning a simple key
  in "txt.yaml", line 2, column 1
could not find expected ':'
  in "txt.yaml", line 3, column 1

但是，如果您更改test.py的第二行：

import ruamel.yaml as yaml
txt = open('txt.yaml').read()
data = yaml.load(txt, yaml.SafeLoader)

你会得到更有趣的错误描述：

...
ruamel.yaml.scanner.ScannerError: while scanning a simple key
  in "<byte string>", line 2, column 1:
    bye
    ^
could not find expected ':'
  in "<byte string>", line 3, column 1:

    ^

这种差异是因为get_mark()（在reader.py中）有更多的上下文指向它是否处理流：

def get_mark(self):
    if self.stream is None:
        return Mark(self.name, self.index, self.line, self.column,
                    self.buffer, self.pointer)
    else:
        return Mark(self.name, self.index, self.line, self.column,
                    None, None)

此数据进入context_mark属性。当您想要为错误提供更多上下文时，请查看它。 但如上所示，仅在从缓冲区解析YAML输入时才有效，而不是从流解析。

搜索YAML源是一项艰巨的任务，各种类的所有方法都附加到它们是父类的Loader或Dumper。最好的帮助跟踪这是在grep上使用def method_name(，因为至少方法名称都是独特的（因为它们必须为此起作用）。

_{在上面我使用了名为ruamel.yaml的增强版PyYAML，为了这个答案的目的，它们应该是一样的。}

如何从PyYAML异常中获取详细信息？

2 个答案: