如何计算列表中特定项目的数量？ Python3

Question

下面的代码将允许用户在列表中输入指定数量的人。 每个人都有三个属性：姓名、性别和年龄。 代码应该计算列表中“m”字符的数量并计算列表中“f”字符的数量，但是当你到达计数行时会出错。 我将如何解决这个问题？

    list1 = []
    person = dict()
    n = int(input("Enter number of elements: "))
    for i in range(0, n):
        print ("Enter information :")
        person[i] = input("Enter name: "), input("Enter sex (m or f): "), input("Enter age: ")
        list1.append(person[i])
        i = i + 1
    print (list1)
    print ("Number of males = " + list1.count('m'))
    print ("Number of females = " + list1.count('f'))

Answer 1

尝试这个：

print("Number of males = " + str([i[1] for i in list1].count("m")))
print("Number of females = " + str([i[1] for i in list1].count('f')))

Answer 2

或者，您可以使用默认模块 «collections» 中的计数器

from collections import Counter

li = [1, 2, 2, 3, 3, 3, 4, 4, 4, 4,]

Counter(li)

这将输出Counter({1: 1, 2: 2, 3: 3, 4: 4}) 。 计数器 output 是一个dict ，但是，您可以更新它或 select 最常见的项目。

Answer 3

这里有几个问题：

• 第二条print指令引发以下错误TypeError: can only concatenate str (not "int") to str 。 这是因为您试图连接 integer 和字符串。 为此，您应该将 integer 转换为如下字符串： print ("Number of males = " + str(list1.count('m')))

• 无论用户输入是什么， list1.count('m')始终为 0，因为list1包含元组，而您正在查找字符串的计数。 您可以通过一个简单的循环获得仅包含性别的列表： [i[1] for i in list1]

固定代码

list1 = []
person = dict()
n = int(input("Enter number of elements: "))
for i in range(0, n):
    print ("Enter information :")
    person[i] = input("Enter name: "), input("Enter sex (m or f): "), input("Enter age: ")
    list1.append(person[i])
    i = i + 1
print (list1)
genders=[i[1] for i in list1]
print("Number of males = " + str(genders.count("m")))
print("Number of females = " + str(genders.count('f')))

Answer 4

使用collections.Counter对对象进行计数。 我还稍微重构了您的代码以实现您的意图：

from collections import Counter
people = []
n = int(input("Enter number of people: "))
for i in range(0, n):
    print ("Enter information:")
    person = (input("Enter name: "),
              input("Enter sex (m or f): "),
              int(input("Enter age: ")))
    people.append(person)
print (people)
c = Counter([p[1] for p in people])
print ("Number of males = " + str(c['m']))
print ("Number of females = " + str(c['f']))

以下是一些评论，其中包含改进代码的建议：

# make variable name more descriptive, for example users or people:
list1 = []

# no need for defining it here, abd BTW it is a tuple later, not dict:
person = dict()

# elements should be more descriptive, for example users or people:
n = int(input("Enter number of elements: "))
for i in range(0, n):
    print ("Enter information :")
    # Add int conversion to age: 'int(input("Enter age: "))'.
    # Also, person[i] should just one person (a single tuple)
    person[i] = input("Enter name: "), input("Enter sex (m or f): "), input("Enter age: ")
    list1.append(person[i])
    # no need for this, since i is incremented in the statement: 'for i in range(0, n)'
    i = i + 1
print (list1)

# Use collections.Counter instead.
# Also count the second element of each element of the list.
print ("Number of males = " + list1.count('m'))
print ("Number of females = " + list1.count('f'))