问题描述
我想知道，为什么在你可以这么做时需要使用 elif ？
I was wondering, why is using elif necessary when you could just do this?
if True:
...
if False:
...
...
推荐答案
当你想确保这个时，你会使用 elif 只挑选一个分支：
You'd use elif when you want to ensure that only one branch is picked:
foo = 'bar'
spam = 'eggs'
if foo == 'bar':
# do this
elif spam == 'eggs':
# won't do this.
与此相比：
foo = 'bar'
spam = 'eggs'
if foo == 'bar':
# do this
if spam == 'eggs':
# *and* do this.
只有 if 语句，选项是非独家。
With just if statements, the options are not exclusive.
当 if 分支更改程序状态时，这也适用 elif 测试也可能是真的：
This also applies when the if branch changes the program state such that the elif test might be true too:
foo = 'bar'
if foo == 'bar':
# do this
foo = 'spam'
elif foo == 'spam':
# this is skipped, even if foo == 'spam' is now true
foo = 'ham'
此处 foo 将设置为'spam'。
foo = 'bar'
if foo == 'bar':
# do this
foo = 'spam'
if foo == 'spam':
# this is executed when foo == 'bar' as well, as
# the previous if statement changed it to 'spam'.
foo = 'ham'
现在 foo 设置为'spam'，然后设置为'ham'。
Now foo is set to 'spam', then to 'ham'.
从技术上讲， elif 是（复合） if 语句的一部分; Python在一系列中选择第一个测试，如果 / elif 测试为true的分支，如果没有，则为 else 分支（如果存在）。使用单独的 if 语句启动新选择，独立于之前的 if 复合语句。
Technically speaking, elif is part of the (compound) if statement; Python picks the first test in a series of if / elif branches that tests as true, or the else branch (if present) if none are true. Using a separate if statement starts a new selection, independent of the previous if compound statement.
这篇关于“if”，“elif”和“elif”。链与普通的“如果”链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！