Reading YAML file with Python results in yaml.composer.ComposerError: expected a single document in the stream

问题

I have a yaml file that looks like

---
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

I am able to read this correctly in Perl using YAML but not in python using YAML. It fails with the error:

expected a single document in the stream

Program:

import yaml

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

Error:

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

回答1:

The yaml documents are separated by ---, and if any stream (e.g. a file) contains more than one document then you should use the yaml.load_all function rather than yaml.load. The code:

import yaml

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

results in for the input file as provided in the question:

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

来源：https://stackoverflow.com/questions/14359557/reading-yaml-file-with-python-results-in-yaml-composer-composererror-expected-a