为什么我的列表只删除两个或多个相同值中的一个?

purified = sequence 不创建的副本 sequence 并分配给 purified

您有几个选择,所有这些都适用于Python2.7

• sequence[:] 称为列表拼接,并对其进行迭代

def purify(sequence):

    #Iterate on copy of sequence
    for i in sequence[:]:
        if i % 2 != 0:
            sequence.remove(i)
    return sequence

print purify([4, 5, 5, 4])
#[4, 4]

• 使用列表理解仅从列表中选择偶数值

def purify(sequence):

    #Pick only even values
    return [item for item in sequence if item%2 == 0]

print purify([4, 5, 5, 4])
#[4, 4]

• filter 过滤出奇数值

def purify(sequence):
    # Iterate on copy of sequence
    return list(filter(lambda x:x%2==0, sequence))

print(purify([4, 5, 5, 4]))
# [4, 4]

迭代时不应尝试移除元素。也, purified = sequence 实际上并没有创建 sequence . 最好的方法是使用这样的列表理解:

def purify(sequence):
    purified = [i for i in sequence if i % 2 == 0]
    return purified

(我本可以发誓我回答了一个骗局,但我找不到……)

不管怎样,原因是您在迭代序列时正在修改它。你应该这样做:

# Python 3
def purify(sequence):
    purified = sequence.copy()
    for i in sequence:
        if i % 2 != 0:
            purified.remove(i)

    return purified

# Python 2
from copy import copy

def purify(sequence):
    purified = copy(sequence)
    for i in sequence:
        if i % 2 != 0:
            purified.remove(i)

    return purified

或者,你可以从一个空的开始 list 并添加满足条件的元素:

def purify(sequence):
    purified = []
    for i in sequence:
        if i % 2 == 0:
            purified.append(i)

    return purified

或者,用 理解,这:

purified = [i for i in sequence if i % 2 == 0]

在python2.7上使用 copy 模块。

from copy import copy

def purify(sequence):
    purified = copy(sequence)
    for i in sequence:
        if i % 2 != 0:
            purified.remove(i)

    return purified
print purify([4, 5, 5, 4])

通过使用

# python 2.x
your_list= filter(lambda x: x % 2 == 0, your_list)

# python 3.x
your_list = list(filter(lambda x: x % 2 == 0, your_list))

print(your_list)

说明:

• 过滤器是用来测试 你的清单

干杯!