yaml文档由分隔---，如果任何流（例如文件）包含多个文档，则应使用yaml.load_all函数而不是yaml.load。编码：
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",
产生问题中提供的输入文件：
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
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