🔒 Combining Multiple Dictionaries into a single Dictionary

[bleak oyster]

# Sets up a dictionary. Heh. Like you'd find in a library.
# It took me an EMBARASSINGLY long time to remember that dictionaries exist, will help!
books = {
    "Fiction": 0,
    "Non-Fiction": 0,
    "Science": 0,
    "History": 0,
    }
     
# Remembering dictionaries existed has GIVEN ME UNLIMITED POWER! Having maximum stock set in a dictionary helps get rid of "magic numbers"
MAXIMUM_STOCK = {
    "Fiction": 30,
    "Non-Fiction": 20,
    "Science": 15,
    "History": 25,
    }```

Part two of my assignment is here, and before I move onto the "first" step, I wanna see if I can combine my two dictionaries here into a single dictionary. Is this possible? I'm aware I will have to change a lot of code down the line, but for my assignment I need to change code anyway, so how can I combine these? Cheers!

[bitter roost]

@bleak oyster

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[bleak oyster]

I feel like something like:

books = {
"Fiction": 30, 0,
"Non-Fiction": 20, 0,
"Science": 15, 0,
"History": 25, 0,
}```

Might be how to do it, but I'm not 100% sure.

Except that gives me an invalid syntax error.

Well actually it's giving me a : expected after dictionary key

Which yeah gives me a syntax error if I try to run.

But if I replace the final commas with colons, it gives me an invalid syntax when it gets to "Non-Fiction".

[mossy totem]

do u know lists/tuples

[bleak oyster]

Somewhat.

I have definitely heard of lists and tuples.

[mossy totem]

so use those for dict values

[bleak oyster]

I'm not 100% sure how to do so in this case.

books = {
    Fiction["1"] = [30, 0]
    Non-Fiction["2"] = [20, 0]
    Science["3"] = [15, 0]
    History["4"] = [25, 0]
    }```

Is this correct?

[mossy totem]

this is closer to correct

[mossy totem]

to make a list u just do [1,2,3,4]

tuples its ()

dict its {} and : btw key,value pairs

just {} would be set, like {1,2,3,4}

[bleak oyster]

I'm a bit confused.

Does the code I posted seem like I'm on the right track?

I need to store the maximum value that the genre can have, as well as be able to add or withdraw books from it.

[bleak oyster]

In that case, what am I doing incorrectly? To me the code I posted seems more like "Combining a dictionary and a list" but I'm not 100% sure.

[grand seal]

this is very close to correct

when you make a list, you put [] around the elements of the list

[bleak oyster]

So then like this? @grand seal?

[grand seal]

kind of

the keys in the first one are correct, the values in the second one are correct

[bleak oyster]

books = {
    "Fiction": [30, 0]
    "Non-Fiction": [20, 0]
    "Science": [15, 0]
    "History": [25, 0]
    }```

This, then?

[grand seal]

yep, one last step now

key value pairs in a dictionaries are separate by commas

[bleak oyster]

As in, a comma after the []?

[grand seal]

yep

[bleak oyster]

"Fiction": [30, 0],

[grand seal]

yes

[bleak oyster]

Very good.

Downside of doing this all is I will have to change a lot of my code 😭

But I think this is more useful in the long run, since I need to both store this in an external file and be able to add new genres.

Am I able to say, modify the numbers in the list using the same code? Or is the fact it's now in a list going to mean I have to change everything?

        else:
            # selected_genre becomes a key with which we can access our dictionary
            # subtracts 1 from the genres so that user input lines up with dictionary.
            selected_genre = genres[selection - 1]
            if books[selected_genre] < MAXIMUM_STOCK[selected_genre]:
                books[selected_genre] += 1
                # Our f-string lets us print the genre and how many books are in it.
                print(f"You have successfully returned a {selected_genre} book.")
                print(f"You now have {books[selected_genre]} {selected_genre} book(s)")
                break
            else:
                print(f"Error 5 ({selection}): Returning exceeds inventory maximum.")```

This for example, is my code which returns a book to the chosen genre.

Obviously, MAXIMUM_STOCK will soon cease to exist, since it's being merged in with the books dictionary.

I'm gonna finish studying for the day, but thanks for the help.

[grand seal]

yes, you can still edit the contents of the dict but with a little more work.
books[selected_genre] becomes books[selected_genre][1] (element at index 1 in the list).
MAXIMUM_STOCK[selected_genre] becomes books[selected_genre][0]

[bleak oyster]

Excellent, thank you so much.

[pale canyon]

!e

d1 = {'A': 1, 'B': 2, 'C': 3, 'D': 4}
d2 = {'A': 6, 'B': 7, 'C': 8, 'D': 9}

d3 = {k: (v, d2[k]) for k, v in d1.items()}

print(d3)

[bitter roost]

:white_check_mark: Your 3.12 eval job has completed with return code 0.

{'A': (1, 6), 'B': (2, 7), 'C': (3, 8), 'D': (4, 9)}

[dark nest]

Using lists like this is a bit annoying - you can improve on the design by making a new type that stores data by name, instead of index:

from dataclasses import dataclass

@dataclass
class Stock:
    held: int
    max: int

books = {
    "Fiction"    : Stock(0, 30),
    "Non-Fiction": Stock(0, 20),
    "Science"    : Stock(0, 15),
    "History"    : Stock(0, 25),
}

for category, stock in books.items():
    print(f"Category: {category}, Stock: {stock.held}/{stock.max}")

That way, you retrieve the max value by saying books[selected_genre].max, instead of books[selected_genre][1] or whichever magic number you chose for that

You can even explicitly clarify which value you're setting, when you make a Stock instance:
Stock(held = 0, max = 30)

[bitter roost]

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