Python列表计数（）方法

Python List count()是Python中的一个内置函数，它返回给定对象在 List 中出现的次数。 count()函数用于对列表和字符串中的元素进行计数。

Syntax: 

list_name.count(object) 

Parameters: 

The object is the things whose count is to be returned. 

Returns: 

count() method returns the count of how many times object occurs in the list.

Exception: 

If more then 1 parameter is passed in count() method, it returns a TypeError.

示例 1：使用 count()  

Python3

# Python3 program to count the number of times
# an object appears in a list using count() method
 
list1 = [1, 1, 1, 2, 3, 2, 1]
 
# Counts the number of times 1 appears in list1
print(list1.count(1))
 
list2 = ['a', 'a', 'a', 'b', 'b', 'a', 'c', 'b']
 
# Counts the number of times 'b' appears in list2
print(list2.count('b'))
 
list3 = ['Cat', 'Bat', 'Sat', 'Cat', 'cat', 'Mat']
 
# Counts the number of times 'Cat' appears in list3
print(list3.count('Cat'))

输出：

4
3
2

示例 2：类型错误

Python3

# Python3 program to demonstrate
# the error in count() method
 
list1 = [1, 1, 1, 2, 3, 2, 1]
 
# Error when two parameters is passed.
print(list1.count(1, 2))

输出：

Traceback (most recent call last):
  File "/home/41d2d7646b4b549b399b0dfe29e38c53.py", line 7, in 
    print(list1.count(1, 2))  
TypeError: count() takes exactly one argument (2 given)

示例 3：计算列表中的元组和列表元素

Python3

# Python3 program to count the number of times
# an object appears in a list using count() method
 
list1 = [ ('Cat', 'Bat'), ('Sat', 'Cat'), ('Cat', 'Bat'),
          ('Cat', 'Bat', 'Sat'), [1, 2], [1, 2, 3], [1, 2] ]
 
# Counts the number of times 'Cat' appears in list1
print(list1.count(('Cat', 'Bat')))
 
# Count the number of times sublist
# '[1, 2]' appears in list1
print(list1.count([1, 2]))

输出：

2
2

实际应用

 假设我们要计算列表中的每个元素并将其存储在另一个列表或字典中。

Python3

# Python3 program to count the number of times
# an object appears in a list using count() method
 
lst = ['Cat', 'Bat', 'Sat', 'Cat', 'Mat', 'Cat', 'Sat']
 
# To get the number of occurrences
# of each item in a list
print ([ [l, lst.count(l)] for l in set(lst)])
 
# To get the number of occurrences
# of each item in a dictionary
print (dict( (l, lst.count(l) ) for l in set(lst)))

输出：

[['Mat', 1], ['Cat', 3], ['Sat', 2], ['Bat', 1]]
{'Bat': 1, 'Cat': 3, 'Sat': 2, 'Mat': 1}