使用Python读取YAML文件时出现yaml.composer.ComposerError: 期望流中有单一文档

Question

我有一个yaml文件，内容如下：

---
level_1: "test"
level_2: 'NetApp, SOFS, ZFS Creation'
request: 341570
---
level_1: "test"
level_2: 'NetApp, SOFS, ZFS Creation'
request: 341569
---
level_1: "test"
level_2: 'NetApp, SOFS, ZFS Creation'
request: 341568

我可以在Perl中正确读取这个文件，使用YAML库没有问题，但在Python中用YAML读取时却失败了。错误信息是：

期望在流中找到一个单独的文档

程序：

import yaml

stram = open("test", "r")
print yaml.load(stram)

错误：

Traceback (most recent call last):
  File "abcd", line 4, in <module>
    print yaml.load(stram)
  File "/usr/local/pkgs/python-2.6.5/lib/python2.6/site-packages/yaml/__init__.py", line 58, in load
    return loader.get_single_data()
  File "/usr/local/pkgs/python-2.6.5/lib/python2.6/site-packages/yaml/constructor.py", line 42, in get_single_data
    node = self.get_single_node()
  File "/usr/local/pkgs/python-2.6.5/lib/python2.6/site-packages/yaml/composer.py", line 43, in get_single_node
    event.start_mark)
yaml.composer.ComposerError: expected a single document in the stream
  in "test", line 2, column 1
but found another document
  in "test", line 5, column 1

Answer 1

yaml文档之间是用---来分隔的。如果一个流（比如一个文件）里面有多个文档，你应该使用yaml.load_all这个函数，而不是yaml.load。下面的代码：

import yaml

stream = open("test", "r")
docs = yaml.load_all(stream, yaml.FullLoader)
for doc in docs:
    for k,v in doc.items():
        print k, "->", v
    print "\n",

对于问题中提供的输入文件，结果是：

request -> 341570
level_1 -> test
level_2 -> NetApp, SOFS, ZFS Creation

request -> 341569
level_1 -> test
level_2 -> NetApp, SOFS, ZFS Creation

request -> 341568
level_1 -> test
level_2 -> NetApp, SOFS, ZFS Creation