带有可选占位符的 string.format() [英] string.format() with optional placeholders

问题描述

我有以下 Python 代码(我使用的是 Python 2.7.X):

I have the following Python code (I'm using Python 2.7.X):

my_csv = '{first},{middle},{last}'
print( my_csv.format( first='John', last='Doe' ) )

我收到 KeyError 异常，因为未指定中间"(这是预期的).但是，我希望所有这些占位符都是可选的.如果未指定这些命名参数，我希望删除占位符.所以上面打印的字符串应该是:

I get a KeyError exception because 'middle' is not specified (this is expected). However, I want all of those placeholders to be optional. If those named parameters are not specified, I expect the placeholders to be removed. So the string printed above should be:

John,,Doe

是否有内置功能使这些占位符可选，或者是否需要进行更深入的工作?如果是后者，如果有人可以向我展示最简单的解决方案，我将不胜感激！

Is there built in functionality to make those placeholders optional, or is some more in depth work required? If the latter, if someone could show me the most simple solution I'd appreciate it!

推荐答案

这是一种选择:

from collections import defaultdict

my_csv = '{d[first]},{d[middle]},{d[last]}'
print( my_csv.format( d=defaultdict(str, first='John', last='Doe') ) )

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