用python做countif的好方法是什么

基于迭代器的方法很好。有一些细微的修改可以强调您正在计算的事实:

sum(1 if meets_condition(x) else 0 for x in my_list)
# or 
sum(1 for x in my_list if meets_condition(x))

和往常一样,如果代码中的意图不明显,则将其封装在描述性命名的函数中:

def count_matching(condition, seq):
    """Returns the amount of items in seq that return true from condition"""
    return sum(1 for item in seq if condition(item))

count_matching(meets_condition, my_list)

第一个

sum(meets_condition(x) for x in my_list)

在我看来,这是一种可读性很强的蟒蛇。

如果你喜欢第二种方法,我会选择的

len(filter(meets_condition, my_list))

另一种方法可能是:

map(meets_condition, my_list).count(True)

列表的countif

#counting if a number or string is in a list
my_list=[1,2,3,2,3,1,1,1,1,1, "dave" , "dave"]
one=sum(1 for item in my_list if item==(1))
two=sum(1 for item in my_list if item==(2))
three=sum(1 for item in my_list if item==(3))
dave=sum(1 for item in my_list if item==("dave"))
print("number of one's in my_list > " , one)
print("number of two's in my_list > " , two)
print("number of three's in my_list > " , three)
print("number of dave's in my_list > " , dave)