在IF语句中使用OR比较 [英] Using OR comparisons with IF statements

问题描述

在Python中使用IF语句时，必须执行以下操作才能使层叠"正常工作.

When using IF statements in Python, you have to do the following to make the "cascade" work correctly.

if job == "mechanic" or job == "tech":
        print "awesome"
elif job == "tool" or job == "rock":
        print "dolt"

在检查等于"时是否有一种方法可以使Python接受多个值?例如，

Is there a way to make Python accept multiple values when checking for "equals to"? For example,

if job == "mechanic" or "tech":
    print "awesome"
elif job == "tool" or "rock":
    print "dolt"

推荐答案

if job in ("mechanic", "tech"):
    print "awesome"
elif job in ("tool", "rock"):
    print "dolt"

括号中的值是一个元组. in运算符检查左侧项目是否出现在右侧手柄元组内部.

The values in parentheses are a tuple. The in operator checks to see whether the left hand side item occurs somewhere inside the right handle tuple.

请注意，当Python使用in运算符搜索元组或列表时，它将进行线性搜索.如果右侧有大量物品，则可能是性能瓶颈.更大范围的方法是使用 frozenset :

Note that when Python searches a tuple or list using the in operator, it does a linear search. If you have a large number of items on the right hand side, this could be a performance bottleneck. A larger-scale way of doing this would be to use a frozenset:

AwesomeJobs = frozenset(["mechanic", "tech", ... lots of others ])
def func():
    if job in AwesomeJobs:
        print "awesome"

如果在程序运行期间不需要更改很棒的作业列表，则首选使用frozenset而不是set.

The use of frozenset over set is preferred if the list of awesome jobs does not need to be changed during the operation of your program.

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