具有可选dict键值的字符串格式 [英] String format with optional dict key-value

问题描述

是否可以使用dict格式化字符串，但是可以选择不存在键错误?

Is there any way to format string with dict but optionally without key errors?

这很好:

opening_line = '%(greetings)s  %(name)s !!!'
opening_line % {'greetings': 'hello', 'name': 'john'}

但是，假设我不知道名字，我想在行上方设置格式仅用于'greetings'.像

But let's say I don't know the name, and I would like to format above line only for 'greetings'. Something like,

 opening_line % {'greetings': 'hello'}

即使:

'hii %(name)s !!!'  # keeping name un-formatted 

但这会在打开包装时显示 KeyError

But this gives KeyError while unpacking

有什么办法吗?

推荐答案

使用 defaultdict ，这将允许您为字典中不存在的键指定默认值.例如:

Use defaultdict, this will allow you to specify a default value for keys which don't exist in the dictionary. For example:

>>> from collections import defaultdict
>>> d = defaultdict(lambda: 'UNKNOWN')
>>> d.update({'greetings': 'hello'})
>>> '%(greetings)s  %(name)s !!!' % d
'hello  UNKNOWN !!!'
>>> 

这篇关于具有可选dict键值的字符串格式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！