Get average for values in a list in a dictionary

Question

I have to create a function called read_data that takes a filename as its only parameter. This function must then open the file with the given name and return a dictionary where the keys are the location names in the file and the values are a list of the readings.

The result of the first function works and displays:

{'Monday': [67 , 43], 'Tuesday': [14, 26], 'Wednesday': [68, 44], ‘Thursday’:[15, 35],’Friday’:[70, 31],’Saturday’;[34, 39],’Sunday’:[22, 18]}

The second function named get_average_dictionary that takes a dictionary structured like the return value of read_data as its only parameter and returns a dictionary with the same keys as the parameter, but with the average value of the readings rather than the list of individual readings. This has to return:

{'Monday': [55.00], 'Tuesday': [20.00], 'Wednesday': [56.00], ‘Thursday’:[25.00],’Friday’:[50.50],’Saturday’;[36.50],’Sunday’:[20.00]}

But I can not get it to work. I get the following errors:

line 25, in <module>
    averages = get_average_dictionary(readings)
line 15, in get_average_dictionary
    average = {key: sum(val)/len(val) for key, val in readings.items()}
AttributeError: 'NoneType' object has no attribute 'items'

Here is the code I have at the moment. Any help would be appreciated.

def read_data(filename):
    readings = {}

    with open("c:\\users\\jstew\\documents\\readings.txt") as f:
        for line in f:
            (key, val) = line.split(',')
            if not key in readings.keys():
                readings[key] = []

            readings[key].append(int(val))

    print(readings)

def get_average_dictionary(readings):
    average = {key: sum(val)/len(val) for key, val in readings.items()}

    print(average)


FILENAME = "readings.txt"

if __name__ == "__main__":
    try:
        readings = read_data(FILENAME)
        averages = get_average_dictionary(readings)


        # Loops through the keys in averages, sorted from that with the largest associated value in averages to the lowest - see https://docs.python.org/3.5/library/functions.html#sorted for details
        for days in sorted(averages, key = averages.get, reverse = True):
            print(days, averages[days])

Answer 1

Given:

di={'Monday': [67 , 43], 'Tuesday': [14, 26], 'Wednesday': [68, 44], 'Thursday':[15, 35],'Friday':[70, 31],'Saturday':[34, 39],'Sunday':[22, 18]}

You can do:

>>> {k:sum(v)/len(v) for k,v in di.items()}
{'Monday': 55.0, 'Tuesday': 20.0, 'Wednesday': 56.0, 'Thursday': 25.0, 'Friday': 50.5, 'Saturday': 36.5, 'Sunday': 20.0}

The error you have seems to be that you are returning nothing from your function. Just do:

def a_func(di):
    return {k:sum(v)/len(v) for k,v in di.items()}

And you should be good to go...

Answer 2

You were close but had at least one problem. One was this:

Friday':[50.50],'Saturday';[36.50],'Sunday': [22, 18]

Notice 'Saturday' is followed by a semicolon, not a colon. That's in both examples. Also, notice your text changes color from red to blue. That usually (this case included) means that you switched from single quotes to something like smartquotes or a character that looks like a normal quote but isn't recognized as such.

{'Monday': [67 , 43], 'Tuesday': [14, 26], 'Wednesday': [68, 44], ‘Thursday’:[15, 35],’Friday’:[70, 31],’Saturday’;[34, 39],’Sunday’:[22, 18]}

Once those are cleared up you just have to deal with the last part, returning vs printing the result.

def get_average_dictionary(readings):
    return {k:(sum(v)/len(v)) for (k,v) in vals.items()}