returning date with traffic intensity from tuples in a list

Question

I'm trying to return all the dates that match with the traffic intensity in the function below but am getting all the elements of only the first tuple as a list instead of all tuples that match.

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

For the test data

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

I am supposed to be getting

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

but instead am getting

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

Can someone please help me with this?

Can you post some sample data that you expect this to work with (i.e `vehicle_records`)? — Joseph M, Apr 17 '18 at 03:27
Just as an FYI, `count >= 5000 and count < 10000` can very neatly be replaced by `5000 <= count < 10000` in Python. Any sequence of rich comparison operators `a op1 b op2 c ...` gets effectively computed as `a op1 b and b op2 c ...`. The only difference is that if `a`, `b` or `c` are complex expressions, they only get evaluated once. — Mad Physicist, Apr 17 '18 at 04:20
Also, you don't need to parenthesize the `if` and `elif` expressions. — Mad Physicist, Apr 17 '18 at 04:21

Primusa · Accepted Answer · 2018-04-17T03:33:58.077

Get the return out of the for loop. Also date_count isn't an array so you should be using .append() not addition:

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

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

There are two issues, one is return is inside for loop which causes to look into only one item. And other is you may need to extend array new_list with date_count. You can try as following:

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] # extend as array
    return new_list # move return

For testing similar scenario, you can consider following example:

l = []
l += "string"
print(l)

Result:

['s', 't', 'r', 'i', 'n', 'g']

Instead:

l = []
l += ["string"]
print(l)

Result:

['string']

For more, I would suggest looking into relevant discussion.

Update:

I think the code can be little shorter with list comprehension and removing condition in elif with following:

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

def dates_with_intensity(vehicle_records, intensity):
    """Returns number of days with the given traffic intensity level"""
    return [date for date, num in vehicle_records if intensity == traffic_intensity(num)]

You can also unpack in a `for`, for more descriptive variable names e.g. `[date for date, num in ... traffic_intensity(num)]` — AChampion, Apr 17 '18 at 04:16
@AChampion (*edited*) thanks! I think it makes more easier to understand. — niraj, Apr 17 '18 at 04:19

returning date with traffic intensity from tuples in a list

2 Answers2

Update: