Pythonic way to make dictionary within a for loop

Question

I am trying to make a dictionary using the output of a function I wrote (dct) that parses an income and spending .csv file. I designated "amount" as the total of the transaction. dct creates a dictionary that returns this:

spending = {
        'month': [],
        'payee': [],
        'amount': [],
        'category': [],
    }

The goal of this next function is to make a dictionary that sums all the "amount" outputs per "category" (only car, home, and food). This is my code so far, and it works. Still, I believe is not the most pythonic way to write it. Any ideas?

def summarize_by_category(dct):
    car, home, food = 0, 0, 0

    for (index,category) in enumerate( dct['category'] ):
        if "car" in category:
            car += dct['amount'][index]
        elif "food" in category:
            food += dct['amount'][index]
        elif "home" in category:
            home += dct['amount'][index]
    Totals = {
        'car': car,
        'food': food,
        'home': home,
    }
    return (Totals)

Why are you using in category instead of == category? Can the category be cars, racecar, etc.? — Barmar
– Barmar, Commented Jun 10, 2020 at 1:21
Things would be easier if you didn't put categories and amounts in separate lists. Use a list of dictionaries: [{"category": "car", "amount": 10, "payee": "gas station", "month": "June"}, ...] — Barmar
– Barmar, Commented Jun 10, 2020 at 1:22

adrtam · Accepted Answer · 2020-06-10 01:26:23Z

2

Not bad, I would say, but you can make this change:

def summarize_by_category(dct):
    Totals = {
        'car': 0,
        'food': 0,
        'home': 0
    }
    for category, amount in zip(dct['category'], dct['amount']):
        for key in Totals:
            if key in category:
                Total[key] += amount
    return (Totals)

So,

You don't reference the list directly. Instead, pair up the amount and cateogry on the fly
You can have more than three categories without much code change: just add the relevant key to the Totals dictionary

Here I assume your category is like "food for John" and "home utilities", if you can do exact match, you should use == instead of in for faster matching.

answered Jun 10, 2020 at 1:26

adrtam

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Barmar Over a year ago

Good idea using zip to pair up categories and amounts

leopardxpreload · Accepted Answer · 2020-06-10 01:37:15Z

1

I am not sure how your dct is structured - but this might be helpful:

def summarize_by_category(dct):
    Totals = {'car': 0, 'home': 0, 'food': 0}

    for index, category in enumerate( dct['category'] ):
        if "car" in category:
            Totals['car'] += dct['amount'][index]
        elif "food" in category:
            Totals['food'] += dct['amount'][index]
        elif "home" in category:
            Totals['home'] += dct['amount'][index]
    return (Totals)

Depending on how your dict is structured, this might work too:

def summarize_by_category(dct):
    return {k: sum(v) for k, v in dct.items()}

edited Jun 10, 2020 at 1:37

answered Jun 10, 2020 at 1:19

leopardxpreload

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1 Comment

Barmar Over a year ago

sums should be Totals

Barmar · Accepted Answer · 2020-06-10 01:25:49Z

You can get rid of all the if/else if you just use the category as the key in the dictionary.

def summarize_by_category(dct):
    totals = {}
    for index, category in enumerate(dct['category']):
        if category in totals:
            totals[category] += dct['amount'][index]
        else:
            totals[category] = dct['amount'][index]
    return totals

If you're only interested in some categories, you can initialize the dictionary with those keys, and skip creating new keys.

def summarize_by_category(dct):
    totals = {'car': 0, 'home': 0, 'food': 0}
    for index, category in enumerate(dct['category']):
        if category in totals:
            totals[category] += dct['amount'][index]
    return totals

MrNobody33 · Accepted Answer · 2020-06-10 03:00:09Z

1

You could try something like this:

def summarize_by_category(dct):
    Totals = {'car': 0, 'home': 0, 'food': 0}

    for i in Totals.keys():
         Totals[i] = sum([dct['amount'][index] for (index,category) in enumerate( dct['category'] ) if i in category ])
    return Totals

Or, if you want a shorter way to do it, you could try something like this:

def summarize_by_category(dct):
    return {i:sum([dct['amount'][index] for (index,category) in enumerate( dct['category'] ) if i in category ]) for i in 'car,home,food'.split(',')}

edited Jun 10, 2020 at 3:00

answered Jun 10, 2020 at 1:26

MrNobody33

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