删除列表中的数字的倍数：

Question

我有两个，我有这个列表，我将如何从该列表中删除数字2的倍数并更新它？

10 [2, 3, 4, 5, 6, 7, 8, 9, 10] 2

Answer 1

Assuming you have a list l and a number n you can remove all multiples of n from l with a list comprehension:

l = [i for i in l if i%n]

writing if i%n here is the same as writing if i%n != 0 , and n divides i iff i%n==0

Answer 2

Methods:

Using a generator

One of the first option that comes to mind is to make use of a generator. The generator would iterate through a sequence, and test if the current element is divisible by n . This allows you to have a more generic solution as well:

def filter_by_multiple(seq, n):
    for i in seq:
        if i % n:
            yield i

Usage:

>>> filter_by_multiple([2, 3, 4, 5, 6, 7, 8, 9, 10], 2)
<generator object filter_by_multiple at 0x000000374ED30258>
>>> list(filter_by_multiple([2, 3, 4, 5, 6, 7, 8, 9, 10], 2))
[3, 5, 7, 9]
>>> 

Using a generator expression

While the above solution is fine, is can be shortened even more by using generator expressions . generator expression are like list comprehensions, but unlike them, they return a generator iterator instead of a list.

Usage:

>>> l = [2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> list(el for el in l if el % 2)
[3, 5, 7, 9]
>>> 

Using filter() :

Among many of the builtin functions in Python, there is one for filtering list called filter() . The usually way to use filter() is to pass in the function you want to use to filter your list, and then the actual list you want filtered. In your case, you want to filter out every element the is not a multiple of two:

Usage:

>>> l = [2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> list(filter(lambda x: x % 2, l))
[3, 5, 7, 9]
>>> 

Using a list comprehension

While all of the above are fine ways for filtering a list, probably the most obvious and canonical, is to use a list comprehension. In your case, your list comprehension, is dead simple.

Usage:

>>> l = [2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> [el for el in l if el % 2]
[3, 5, 7, 9]
>>>