I'm trying to do a simple math by removing one book copy from my library every time some one lo-CodePudding

This is the line that makes me all the trouble, My question is how can I remove one int(number) from books_library?

example of my book_library:

    {'Books': 
[{"Book's ID": {'003'},
 "Book's Name": {'Avengers'},
 "Book's Authors": {'Stan Lee, Jack Kirby'},
 "Book's Published year": {'1939'},
 "Book's Type": {'1'},
 "Book's Copies": {15}}

books_library["Books"][book]["Book's Copies"][0] = books_library["Books"][book]["Book's Copies"][0] - 1

Returns me an Error : TypeError: 'set' object is not subscriptable

 with open('loans_data.pkl', 'wb') as loans_save:
    for book in range(len(books_library["Books"])):
        if book_name_input in books_library["Books"][book]["Book's Name"]:
            books_library["Books"][book]["Book's Copies"][0] = books_library["Books"][book]["Book's Copies"][0] - 1
            book_details = {"ID":books_library["Books"][book]["Book's ID"],
                            "Name":books_library["Books"][book]["Book's Name"],
                            "Author":books_library["Books"][book]["Book's Author"]}
            for customer in range(len(customers_library["Customers"])):
                if customer_name_input in customers_library["Customers"][customer]["Customer's Name"]:
                    customer_details = {"Name": customers_library["Customers"][customer]["Customer's Name"],
                                        "ID": customers_library["Customers"][customer]["Customer's ID"]}
                    loan_library["Customer"].update({customer_details:{book_details}})
                    pickle.dump(loan_library, loans_save)

CodePudding user response：

Due to documentation set data structure is unordered collections of unique elements and that doesn't support operations like indexing or slicing etc.

>>> test_set = {1, 2, 3}
>>> test_set[0]
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: 'set' object is not subscriptable

In your case books_library["Books"][book]["Book's Copies"] is set, so you should change it to list or another type that you want (looks like it should be just integer).

CodePudding user response：

An important thing to learn is to pay attention to what exactly those errors say. They are intended to be helpful. Here, for example, it says

TypeError: 'set' object is not subscriptable

So what does subscriptable mean? Simplified, to get an item from a sequence or dictionary, or a user defined object by using a key or index. This is taken straight from the python docs. See here. But it says set is not subscriptable. So you go and look up what exactly a set is in the docs, and there you find out that its a builtin data structure that does not support subscription. And you see that the syntax for creating a set is {itemlist}. So you have just used sets for all the values in you dictionary, with unintended side effects! The solution is to not to use sets - storing different kinds of data in a dict works exactly as it would normally: {key: 1} stores and int(1), {key: [1,2]} a list and so on, so in your example you would use

"Book's Copies": 15

Conclusion: Listen to what python tries to tell you and use the docs, they are excellent.