Python字典理解中的条件表达式

Question

a = {"hello" : "world", "cat":"bat"}

# Trying to achieve this
# Form a new dictionary only with keys with "hello" and their values
b = {"hello" : "world"}

# This didn't work

b = dict( (key, value) if key == "hello" for (key, value) in a.items())

关于如何在字典理解中包含条件表达式以决定是否应将键元组值包含在新字典中的任何建议

Answer 1

移动if到底:

b = dict( (key, value) for (key, value) in a.items() if key == "hello" )

你甚至可以使用dict-comprehension(dict(...)不是一个,你只是使用dict工厂而不是生成器表达式):

b = { key: value for key, value in a.items() if key == "hello" }

Answer 2

您不需要使用字典理解:

>>> a = {"hello" : "world", "cat":"bat"}
>>> b = {"hello": a["hello"]}
>>> b
{'hello': 'world'}

而dict(...)不是字典解析.