我想从列表中删除一个值,如果它存在于列表中(它可能不存在)。

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]
print(a)

上面给出了错误:

ValueError: list.index(x): x not in list

所以我必须这样做:

a = [1, 2, 3, 4]

try:
    b = a.index(6)
    del a[b]
except:
    pass

print(a)

难道没有更简单的方法吗?


当前回答

 list1=[1,2,3,3,4,5,6,1,3,4,5]
 n=int(input('enter  number'))
 while n in list1:
    list1.remove(n)
 print(list1)

其他回答

另一种可能是使用set而不是list,如果set适用于您的应用程序。

IE中如果你的数据不是有序的,并且没有副本,那么

my_set=set([3,4,2])
my_set.discard(1)

是没有错误的。

通常,列表只是一个方便的容器,用于存放实际上是无序的项目。有些问题询问如何从列表中删除一个元素的所有出现。如果你一开始就不想被骗,一套也很方便。

my_set.add(3)

不改变上面的my_set。

通常,如果你告诉Python做一些它不能做的事情,Python会抛出一个异常,所以你必须这样做:

if c in a:
    a.remove(c)

or:

try:
    a.remove(c)
except ValueError:
    pass

异常不一定是坏事,只要它是您所期望的并正确处理的。

通过索引除希望删除的元素之外的所有内容来覆盖列表

>>> s = [5,4,3,2,1]
>>> s[0:2] + s[3:]
[5, 4, 2, 1]

更普遍的是,

>>> s = [5,4,3,2,1]
>>> i = s.index(3)
>>> s[:i] + s[i+1:]
[5, 4, 2, 1]

一些最简单的基准测试方法:

import random
from copy import copy
sample = random.sample(range(100000), 10000)
remove = random.sample(range(100000), 1000)

%%timeit
sample1 = copy(sample)
remove1 = copy(remove)

for i in reversed(sample1):
    if i in remove1:
        sample1.remove(i)
# 271 ms ± 16 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# remove all instances

%%timeit
sample1 = copy(sample)
remove1 = copy(remove)

filtered = list(filter(lambda x: x not in remove1, sample1))
# 280 ms ± 18.9 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# remove all instances

%%timeit
sample1 = copy(sample)
remove1 = copy(remove) 

filtered = [ele for ele in sample1 if ele not in remove1]
# 293 ms ± 72.1 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# remove all instances

%%timeit
sample1 = copy(sample)
remove1 = copy(remove) 

for val in remove1:
    if val in sample1:
        sample1.remove(val)
# 558 ms ± 40.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# only remove first occurrence

%%timeit
sample1 = copy(sample)
remove1 = copy(remove) 

for val in remove1:
    try:
        sample1.remove(val)
    except:
        pass
# 609 ms ± 11.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# only remove first occurrence

使用一个for循环和一个条件:

def cleaner(seq, value):    
    temp = []                      
    for number in seq:
        if number != value:
            temp.append(number)
    return temp

如果你想删除一些,但不是全部:

def cleaner(seq, value, occ):
    temp = []
    for number in seq:
        if number == value and occ:
            occ -= 1
            continue
        else:
            temp.append(number)
    return temp