Python:根据长度删除列表中的字符串对象 [英] Python: deleting a string object in a list based on the length

问题描述

如果字符数为5个或更少，我想从列表中删除每个城市.

I want to delete each city from the list if the number of the characters is 5 or less.

cities = ["New York", "Shanghai", "Munich", "Toyko", "Dubai"]
j = 0
for i in cities:
    if len(i) <= 5:
        del cities[j]
    j += 1

这仅删除5个字符以内的第一个城市.但第二个不是.

That deletes only the first city which is 5 characters or less. But not the second one.

我也尝试过:

i = 0
while i < len(cities):
    if len(cities[i]) <= 5:
        del cities[i]
    i += 1

但是它给了我相同的结果！

but it gave me the same result!!

更新: 最简单的方法是添加一个切片:

UPDATE: The easiest way to do it is just to add a slice:

for i in cities[:]:
        if len(i) <= 5:
            cities.remove(i)       

# output: ["New York", "Shanghai", "Munich"]

推荐答案

您所描述的称为参考透明的Wiki文章是一个很好的起点.

What you're describing is known as a Filter operation. You should look at the docs. The following code uses it to generate a brand new list of city names in a single line of code. Constructing a new list will prevent you from a whole class of mistakes that you can make while mutating your memory. The wiki article on Referential Transparency is a good starting point.

cities = ["New York", "Shanghai", "Munich", "Toyko", "Dubai"]

citiesWithLongNames = filter (lambda cityName: len (cityName) > 5, cities)

print (citiesWithLongNames) # => ['New York', 'Shanghai', 'Munich']

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您还应该阅读所有内置函数，并且您会发现python中已经内置了很多东西，使您不必手动实现琐碎的事情.

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You should also read up on all the built in functions, and you'll find that there is a bunch of stuff built into python already that keeps you from having to implement trivialities manually.

奖励:使用列表理解:

print ([city for city in cities if len (city) > 5])

比嵌套循环干净得多. :)

Much cleaner than nested loops. :)

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