python中count是什么意思 python计数方法功能解析

# 列表中的count方法
numbers = [1, 2, 3, 2, 4, 2, 5]
count_of_twos = numbers.count(2)
print(count_of_twos)  # 输出: 3

# 字符串中的count方法
text = "hello world, hello python"
count_of_hello = text.count("hello")
print(count_of_hello)  # 输出: 2

# 区分大小写
text = "Hello hello HELLO"
count_of_hello = text.count("hello")
print(count_of_hello)  # 输出: 1

# 性能对比
import time

large_list = [1] * 1000000
large_string = "a" * 1000000

# 使用count方法
start_time = time.time()
count_result = large_list.count(1)
print(f"Count method time: {time.time() - start_time}")

# 使用in操作符
start_time = time.time()
in_result = 1 in large_list
print(f"In operator time: {time.time() - start_time}")

# 使用count方法
start_time = time.time()
count_result = large_string.count("a")
print(f"Count method time: {time.time() - start_time}")

# 使用in操作符
start_time = time.time()
in_result = "a" in large_string
print(f"In operator time: {time.time() - start_time}")

# 使用列表的count方法统计字典值的出现次数
my_dict = {'a': 1, 'b': 2, 'c': 1, 'd': 3, 'e': 2}
value_list = list(my_dict.values())
count_of_ones = value_list.count(1)
print(count_of_ones)  # 输出: 2

# 使用collections.Counter
from collections import Counter

value_counter = Counter(my_dict.values())
print(value_counter[1])  # 输出: 2

from datetime import datetime

login_times = [
    datetime(2023, 10, 1, 8, 0),
    datetime(2023, 10, 1, 9, 0),
    datetime(2023, 10, 1, 10, 0),
    datetime(2023, 10, 2, 8, 0),
    datetime(2023, 10, 2, 9, 0),
]

morning_logins = sum(1 for time in login_times if time.hour < 12)
print(f"Morning logins: {morning_logins}")  # 输出: 5