Loop through function and auto-generate dictionary

Question

I'm trying to make my code more 'Pythonic'.

At the moment I am calling a function 16 times, incrementing by 12 each time. I then add these variables to a dictionary and assign a key with the same name as the variable (value):

        c1 = getIndividualCounts(42)
        c2 = getIndividualCounts(54)
        c3 = getIndividualCounts(66)
        c4 = getIndividualCounts(78)
        c5 = getIndividualCounts(90)
        c6 = getIndividualCounts(102)
        c7 = getIndividualCounts(114)
        c8 = getIndividualCounts(126)
        c9 = getIndividualCounts(138)
        c10 = getIndividualCounts(150)
        c11 = getIndividualCounts(162)
        c12 = getIndividualCounts(174)
        c13 = getIndividualCounts(186)
        c14 = getIndividualCounts(198)
        c15 = getIndividualCounts(210)
        c16 = getIndividualCounts(222)

        main_data = {'c1':c1, 'c2':c2, 'c3':c3, 'c4':c4, 'c5':c5, 'c6':c6, 'c7':c7, 'c8':c8, 'c9':c9, 'c10':c10, 'c11':c11, 'c12':c12, 'c013':c13, 'c14':c14, 'c15':c15, 'c16':c16}

This currently works fine, but is quite chunky. What I would like to do is the loop through the function 16 times, increasing the start index by 12 each time and auto-generating the dictionary and keys + values.

This is what I have so far:

        index = 1
        for i in range(16):
            index += 12
            getIndividualCounts(42) + index
            return ({'c' + str(i) + ':'+ c + i} )

Needless to say it doesn't work. I've tried multiple iterations, but can't find any approach that works. As a relatively new Python programmer, I would also appreciate an explanation to a possible solution, so I can learn going forward.

This question has already been answered here: https://stackoverflow.com/questions/701802/how-do-i-execute-a-string-containing-python-code-in-python — Elisha Kupietzky, Oct 01 '20 at 10:39
You should work through the [Python tutorial](https://docs.python.org/3/tutorial/) if not done yet. It has examples how to use dictionaries and about the "range" function among many more helpful things. — Michael Butscher, Oct 01 '20 at 10:41

score 1 · Accepted Answer · answered Oct 01 '20 at 10:46

1

This is a possible solution

main_data = dict()
inital_value = 42

for i in range(16):
    index = 'c{}'.format(i+1)
    value = inital_value + i*12
    main_data[index] = getIndividualCounts(value)
    print(index, value)

answered Oct 01 '20 at 10:46

Pixel_teK

793
5
16

Yeah this worked a treat. I made some tweaks to make initial_value a dictionary entry, but otherwise all good. Thanks! – red_sach Oct 05 '20 at 08:02

score 0 · Answer 2 · answered Oct 01 '20 at 10:44

Don't use these intermediate variables, just build the dict directly:

main_data = {}

for index in range(1, 17):
    main_data['c' + str(index)] = getIndividualCounts(30 + 12*index)

or with a dict comprehension:

main_data = {'c' + str(index): getIndividualCounts(30 + 12*index) for index in range(1, 17)}

Note that, more generally, if you feel the need to have some related variables like you did in the first part of your code, you should use a list or a dict to put them in a structure, not have independant variables just related by their name.

score 0 · Answer 3 · answered Oct 01 '20 at 10:44

The code with explanations:

# your function you want to call:
def getIndividualCounts(x):
    return x

# the dictionary where you want to store data
main_data = {}

# the loop, i goes from 0, 1, ... to 15
for i in range(16):
    key = 'c{}'.format(i+1)                 # create key (c1, c2, c3, ...)
    value = getIndividualCounts(42 + i*12)  # create value by calling the function (42, 54, ...)

    # store the key, value inside the dictionary
    main_data[key] = value

# print the data:
print(main_data)

Prints:

{'c1': 42, 'c2': 54, 'c3': 66, 'c4': 78, 'c5': 90, 'c6': 102, 'c7': 114, 'c8': 126, 'c9': 138, 'c10': 150, 'c11': 162, 'c12': 174, 'c13': 186, 'c14': 198, 'c15': 210, 'c16': 222}

score 0 · Answer 4 · answered Oct 01 '20 at 10:45

main_data = {}
for counter, val in enumerate(range(42, 222+1, 12)):
    main_data[f'c{counter+1}'] = getIndividualCounts(val)

This would achive what you are looking for. f'' refers to format string. So you can insert varibles inside string by putting them in {}

Loop through function and auto-generate dictionary

4 Answers4