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?
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
这就是我的答案,用while和for就可以了
def remove_all(data, value):
i = j = 0
while j < len(data):
if data[j] == value:
j += 1
continue
data[i] = data[j]
i += 1
j += 1
for x in range(j - i):
data.pop()
其他回答
这将从数组sys中删除"-v"的所有实例。Argv,如果没有找到实例,则不报错:
while "-v" in sys.argv:
sys.argv.remove('-v')
你可以在一个名为speechToText.py的文件中看到代码的运行:
$ python speechToText.py -v
['speechToText.py']
$ python speechToText.py -x
['speechToText.py', '-x']
$ python speechToText.py -v -v
['speechToText.py']
$ python speechToText.py -v -v -x
['speechToText.py', '-x']
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
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。
在列表中查找一个值,然后删除该索引(如果它存在的话),使用list的remove方法更容易完成:
>>> a = [1, 2, 3, 4]
>>> try:
... a.remove(6)
... except ValueError:
... pass
...
>>> print a
[1, 2, 3, 4]
>>> try:
... a.remove(3)
... except ValueError:
... pass
...
>>> print a
[1, 2, 4]
如果你经常这样做,你可以把它包在一个函数中:
def remove_if_exists(L, value):
try:
L.remove(value)
except ValueError:
pass
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