Question

如何查找任意列表中是否存在偶数个元素或奇数个元素。

我尝试了list.index（）以获取所有索引......但我仍然不知道如何告诉程序什么是偶数和什么是奇数。

Answer 1

您可以使用内置函数len()。

获取任意列表的长度（元素数）。

myList = [0,1,2,3,4,5]

if len(myList) % 2 == 0:
    print ("even")
else
    print ("odd")

定义返回bool（true或false）的函数。

def is_even(myList):

    if len(myList) % 2 == 0:
        return true
    else:
        return false

main():

    myList = [0,1,2,3]
    theListIsEven = is_even(myList)  # will be true in this example
                                     # because 4 items in myList

    if theListIsEven(myList) == True:
        # do something
    else:
        # do something else

    return 0

模数运算符 % 给出余数。

EX：7％2 = 1

最接近7的2将均分为6
距离7是1。
因此，剩余1为7％2。

EX：4％2 = 0

当n％2
因为n平均分为2

Answer 2

你需要的只是

len(listName)

这将为您提供长度。

我想你也可以这样做

if len(listName) % 2 == 0:
    return True  # the number is even!
else:
    return False # the number is odd!

Answer 3

your_list = [1,2,3,(4,5)]

# modulo operation finds the remainder of division of one number by another.
if len(your_list) % 2 == 0:
    print "Even Number"
else:
    print"number is odd"

Answer 4

if len(mylist)%2==0:
     #even
else:
     #odd

Answer 5

def has_even_length(some_sequence):
    return not len(some_sequence)%2

def has_odd_length(some_sequence):
    return bool(len(some_sequence)%2)

Answer 6

偶数可以被2整除。奇数不是。

len(X)将获得X

的长度

如果X的长度可被2整除，那么它是偶数如果X的长度不能被2整除，那么它就是奇数

len(X)%2返回除法问题的“余数”

例如5%2将返回非{0}的1（因为5除以2是2，余数为1）因此它不是偶数。与6%4相同的是返回2，因为6除以4是1，余数为2。

所以len(X)%2 X是你的列表，将返回1，表示它是奇数，或者0表示它是偶数。

Answer 7

如果您想对此有所了解，也可以使用。

if len(mylist)&1:
    print("odd")
else:
    print("even")

如果您知道您的列表更有可能是奇怪的，这真是好看。

if len(mylist)&1:
    print("list was odd")
elif CheckSomthingElse():
    print("list was even AND CheckSomthingElse was True")
else:
    print("list was even AND CheckSomthingElse was False")

通过％2以下的测试在python中哇更快。 python必须为此进行优化。在某些其他语言中，＆1更快。这就是为什么始终进行测试很重要的原因。

import timeit

MyListOdd=[1,2,3,4,5,6,7]
MyListEven=[1,2,3,4,5,6]
print("MyListOdd  == ",MyListOdd)
print("MyListEven == ",MyListEven)
print("len(MyListOdd)  == ",len(MyListOdd))
print("len(MyListEven) == ",len(MyListEven))

def TestIfEvenBitwise(MyList):
    if len(MyList)&1:
        return False #Odd
    else:
        return True #Even

def TestIfEvenModulus(MyList):
    if len(MyList)%2:
        return False #Odd
    else:
        return True #Even

print("TestIfEvenBitwise(MyListOdd)  == ",TestIfEvenBitwise(MyListOdd))
print("TestIfEvenModulus(MyListOdd)  == ",TestIfEvenModulus(MyListOdd))
print("TestIfEvenBitwise(MyListEven) == ",TestIfEvenBitwise(MyListEven))
print("TestIfEvenModulus(MyListEven) == ",TestIfEvenModulus(MyListEven))

mysetup = """
MyListOdd=[1,2,3,4,5,6,7]
MyListEven=[1,2,3,4,5,6]

def TestIfEvenBitwise(MyList):
    if len(MyList)&1:
        return False #Odd
    else:
        return True #Even

def TestIfEvenModulus(MyList):
    if len(MyList)%2:
        return False #Odd
    else:
        return True #Even
"""

print("timeit.timeit(setup = mysetup,stmt ='TestIfEvenBitwise(MyListOdd)', number=100000) == ",
      timeit.timeit(setup = mysetup,stmt ='TestIfEvenBitwise(MyListOdd)', number=100000))
print("timeit.timeit(setup = mysetup,stmt ='TestIfEvenModulus(MyListOdd)', number=100000) == ",
      timeit.timeit(setup = mysetup,stmt ='TestIfEvenModulus(MyListOdd)', number=100000))
print("timeit.timeit(setup = mysetup,stmt ='TestIfEvenBitwise(MyListEven)', number=100000) == ",
      timeit.timeit(setup = mysetup,stmt ='TestIfEvenBitwise(MyListEven)', number=100000))
print("timeit.timeit(setup = mysetup,stmt ='TestIfEvenModulus(MyListEven)', number=100000) == ",
      timeit.timeit(setup = mysetup,stmt ='TestIfEvenModulus(MyListEven)', number=100000))

测试结果。

MyListOdd  ==  [1, 2, 3, 4, 5, 6, 7]
MyListEven ==  [1, 2, 3, 4, 5, 6]
len(MyListOdd)  ==  7
len(MyListEven) ==  6
TestIfEvenBitwise(MyListOdd)  ==  False
TestIfEvenModulus(MyListOdd)  ==  False
TestIfEvenBitwise(MyListEven) ==  True
TestIfEvenModulus(MyListEven) ==  True
timeit.timeit(setup = mysetup,stmt ='TestIfEvenBitwise(MyListOdd)', number=100000) ==  0.02574796500000004
timeit.timeit(setup = mysetup,stmt ='TestIfEvenModulus(MyListOdd)', number=100000) ==  0.022446242000000005
timeit.timeit(setup = mysetup,stmt ='TestIfEvenBitwise(MyListEven)', number=100000) ==  0.026081517000000054
timeit.timeit(setup = mysetup,stmt ='TestIfEvenModulus(MyListEven)', number=100000) ==  0.025758655999999935

Answer 8

使用模数运算符 - %给出余数。为了得到均匀，你需要除以2，例如：

7 % 2 = 1
8 % 2 = 0

最蟒蛇的方式是：

def is_even(your_list):
    if len(your_list) % 2:  # 0 in case of even i.e. No remainder
        return True
    else:
        return False

如何知道列表中的偶数个数或奇数

8 个答案: