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

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

当nums是列表,c是要删除的值时:

要删除列表中第一个出现的c,只需执行以下操作:

if c in nums:
    nums.remove(c)

要从列表中删除所有出现的c,请执行以下操作:

while c in nums:
    nums.remove(c)

添加异常处理将是最佳实践,但我主要想演示如何从列表中删除所有出现的元素。

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。

以下是如何做到这一点(不需要理解列表):

def remove_all(seq, value):
    pos = 0
    for item in seq:
        if item != value:
           seq[pos] = item
           pos += 1
    del seq[pos:]

如果你的元素是不同的,那么一个简单的集合差异就可以了。

c = [1,2,3,4,'x',8,6,7,'x',9,'x']
z = list(set(c) - set(['x']))
print z
[1, 2, 3, 4, 6, 7, 8, 9]