在python lambda函数中使用OR运算符 [英] Use of OR operator in python lambda function

问题描述

O Reilly编程Python书中有一个代码示例，该代码示例在lambda函数中使用OR运算符.文字指出"[[代码]使用or运算符强制两个表达式运行".

There is a code example in the O Reilly Programming Python book which uses an OR operator in a lambda function. The text states that "[the code] uses an or operator to force two expressions to be run".

这如何以及为什么起作用?

How and why does this work?

widget = Button(None, # but contains just an expression
text='Hello event world',
command=(lambda: print('Hello lambda world') or sys.exit()) )
widget.pack()
widget.mainloop()

推荐答案

Python中的每个函数都返回一个值.如果没有显式的return语句，它将返回None. None作为布尔表达式的结果为False.因此，print返回None，并且总是评估or表达式的右侧.

Every funnction in Python returns a value. If there is no explicit return statement it returns None. None as boolean expression evaluates to False. Thus, print returns None, and the right hand side of the or expression is always evaluated.

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