使用带有 Yaml 文件的 Python f 字符串? [英] Leverage Python f-strings with Yaml files?

问题描述

如果我有一个 yaml 文件，其中包含一个带有括号符号 {} 的字符串，与 python f-strings 一起使用，这里如何利用 f-string 插值?以这个简单的 yaml 文件为例:

If I have a yaml file containing a string with the bracket notation {} used in partnership with python f-strings, how might a leverage the f-string interpolation here? Take for example this simple yaml file:

# tmp.yaml
k1: val1
k2: val2 as well as {x}

如果x = 'val3'，我希望k2的值反映val2以及val3

If x = 'val3', I would like the value of the k2 to reflect val2 as well as val3

# app.py
x = 'val3'
with open('tmp.yaml', 'rt') as f:
    conf = yaml.safe_load(f)

print(conf)
{'k1': 'val1', 'k2': 'val2 as well as {x}'}

这可以用格式字符串很容易地完成...

This could be accomplished pretty easily with format strings...

print(conf['k2'].format(x=x))
val2 as well as val3

但是如何对 f-strings 做同样的事情?

But how to do the same with f-strings?

推荐答案

您可以定义自定义构造函数:

You can define a custom constructor:

import yaml

values = { 'x': 'val3' }

def format_constructor(loader, node):
  return loader.construct_scalar(node).format(**values)

yaml.SafeLoader.add_constructor(u'!format', format_constructor)

conf = yaml.safe_load("""
k1: val1
k2: !format val2 as well as {x}
""")

print(conf)

如果不想使用标签 !format，也可以使用 add_constructor 和 u'tag:yaml.org,2002:str' 作为标签.这将使用您的默认字符串构造函数覆盖.

If you don't want to use the tag !format, you can also use add_constructor with u'tag:yaml.org,2002:str' as tag. This will override the default string constructor with yours.

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