python - 从列表中的元组返回具有流量强度的日期

Question

我试图在下面的函数中返回与流量强度匹配的所有日期，但我只将第一个元组的所有元素作为列表而不是所有匹配的元组。

def traffic_intensity(count):
   """Returns string indicating intensity level given by number of 
    vehicles"""
    level_name = ""
    if(count < 5000):
        level_name = "Very Low"
    elif(count >= 5000 and count < 10000):
        level_name = "Low"
    elif(count >= 10000 and count < 18000):
       level_name = "Moderate"
    elif(count >= 18000):
        level_name = "High"
    return(level_name)


def dates_with_intensity(vehicle_records, intensity):
    """Returns number of days with the given traffic intensity level"""
    new_list = []
    for number in vehicle_records:
        date_count = number[0]
        number_count = number[1]
        traffic = traffic_intensity(number_count)
        if traffic == intensity:
            new_list += date_count
        return new_list

对于测试数据

vehicle_records = [('2010-01-01',1),
                ('2010-01-02',2),
                ('2010-01-03',3)]
days = dates_with_intensity(vehicle_records, 'Very Low')
print(days)

我应该得到

['2010-01-01', '2010-01-02', '2010-01-03']

但我得到了

['2', '0', '1', '0', '-', '0', '1', '-', '0', '1']

有人可以帮我解决这个问题吗？

Answer 1

从 for 循环中获取返回值。 date_count 也不是数组，所以你应该使用 .append() 而不是加法:

def dates_with_intensity(vehicle_records, intensity):
"""Returns number of days with the given traffic intensity level"""
    new_list = []
    for number in vehicle_records:
        date_count = number[0]
        number_count = number[1]
        traffic = traffic_intensity(number_count)
        if traffic == intensity:
            new_list.append(date_count)
    return new_list