是否可以在YAML中执行字符串替换？

您无法真正替换YAML中的字符串值，例如，某个字符串的子字符串将替换为另一个子字符串¹. 但是，YAML可以标记节点（在您的情况下，列表['a'，'b'，'c']并再次使用.

锚点的格式为＆some_id，并在* some_id（不是节点）指定节点和别名节点之前插入.

这与字符串级替换不同，因为在解析YAML文件期间，可以保留引用. 就像在Python中为集合类型上的所有锚点加载YAML一样（例如cmd替换字符串，在标量上使用锚点时）:

import sys
import ruamel.yaml as yaml
yaml_str = """\
sub: &sub0 [a, b, c]
command:
    params:
        cmd1:
            type: string
            # Get the list defined in 'sub'
            enum : *sub0
            description: Exclude commands from the test list.
        cmd2:
            type: string
            # Get the list defined in 'sub'
            enum: *sub0
"""
data1 = yaml.load(yaml_str, Loader=yaml.RoundTripLoader)
# the loaded elements point to the same list
assert data1['sub'] is data1['command']['params']['cmd1']['enum']
# change in cmd2
data1['command']['params']['cmd2']['enum'][3] = 'X'
yaml.dump(data1, sys.stdout, Dumper=yaml.RoundTripDumper, indent=4)

这将输出:

sub: &sub0 [a, X, c]
command:
    params:
        cmd1:
            type: string
            # Get the list defined in 'sub'
            enum: *sub0
            description: Exclude commands from the test list.
        cmd2:
            type: string
            # Get the list defined in 'sub'
            enum: *sub0

请注意，原始锚点名称仍然存在.

如果您不想在输出中使用锚点和别名，则可以在RoundTripDumper的RoundTripRepresenter子类中重写ignore_aliases方法（该方法有两个参数，但使用lambda * args: ...您不必须知道）: <

dumper = yaml.RoundTripDumper
dumper.ignore_aliases = lambda *args : True
yaml.dump(data1, sys.stdout, Dumper=dumper, indent=4)

这使得:

sub: [a, X, c]
command:
    params:
        cmd1:
            type: string
            # Get the list defined in 'sub'
            enum: [a, X, c]
            description: Exclude commands from the test list.
        cmd2:
            type: string
            # Get the list defined in 'sub'
            enum: [a, X, c]

此技术可用于读取YAML文件，就好像您已完成字符串替换一样cmd替换字符串，通过重新读取转储的材料来忽略别名:

data2 = yaml.load(yaml.dump(yaml.load(yaml_str, Loader=yaml.RoundTripLoader),
                    Dumper=dumper, indent=4), Loader=yaml.RoundTripLoader)
# these are lists with the same value
assert data2['sub'] == data2['command']['params']['cmd1']['enum']
# but the loaded elements do not point to the same list
assert data2['sub'] is not data2['command']['params']['cmd1']['enum']
data2['command']['params']['cmd2']['enum'][5] = 'X'
yaml.dump(data2, sys.stdout, Dumper=yaml.RoundTripDumper, indent=4)

现在只有一个“ b”变成了“ X”:

sub: [a, b, c]
command:
    params:
        cmd1:
            type: string
            # Get the list defined in 'sub'
            enum: [a, b, c]
            description: Exclude commands from the test list.
        cmd2:
            type: string
            # Get the list defined in 'sub'
            enum: [a, X, c]

如上所述，仅当在集合类型上使用锚/别名时才需要，而在标量上使用时则不需要.

¹由于YAML可以创建对象，因此可能会产生影响

解析器是否创建了这些对象. 介绍如何执行此操作. 保留名称最初不可用，但已在ruamel.yaml更新中实现.

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