How to create a nested dictionary comprehensions?-CodePudding

How to convert the following code into a nested comprehensions?

new_dict = {'Accounts': 'lbl1', 'Inventory': 'lbl2', 'Manufacture': 'lbl3', 'PayRoll': 'lbl4', 'kannagu': 'lbl1', 'Saragu': 'lbl2', 'Thayarippu': 'lbl3', 'Sambalam': 'lbl4', 'F1': 'lbl1', 'F2': 'lbl2', 'F3': 'lbl3', 'F4': 'lbl4'}

dict_keys = {'name': {'lbl1': 'label1', 'lbl2': 'label2', 'lbl3': 'label3', 'lbl4': 'label4'}, 'item3': {'lbl1': 'F1', 'lbl2': 'F2', 'lbl3': 'F3', 'lbl4': 'F4'}, 'item2': {'lbl1': 'kannagu', 'lbl2': 'Saragu', 'lbl3': 'Thayarippu', 'lbl4': 'Sambalam'}, 'item1': {'lbl1': 'Accounts', 'lbl2': 'Inventory', 'lbl3': 'Manufacture', 'lbl4': 'PayRoll'}, 'printitem': {'lbl1': 'You clicked label1', 'lbl2': 'You clicked label2', 'lbl3': 'You clicked label3', 'lbl4': 'You clicked label4'}}

for key,val in new_dict.items():
        if key == Accounts:
            for k, v in dict_key['printitem'].items():
                if k == val :
                    print(v)

CodePudding user response：

Dictionary comprehensions are useful for creating a dictionaries compactly. They need to result in a new dictionary, and they shouldn't have side effects like printing values. This code doesn't create a dictionary, so they're not suitable here.

You actually don't need either of the loops. Both of them are just looking up a key in a dictionary, which can be done with a simple d[key] or d.get(key) lookup. You can simplify this code to:

if val := new_dict.get(sending_button.text()):
    if v := dict_key['printitem'].get(val):
        print(v)

If you're not using Python 3.8 then you can use this longer version without the := walrus operator:

val = new_dict.get(sending_button.text())
if val:
    v = dict_key['printitem'].get(val)
    if v:
        print(v)

CodePudding user response：

If you want v to be in separated nested list per for k, v

[[v for k, v in dict_key['printitem'].items() if k == val] for key, val in new_dict.items() if key == sending_button.text()]

If you want v to be stored in one large list

[v for key, val in new_dict.items() if key == sending_button.text() for k, v in dict_key['printitem'].items() if k == val]

CodePudding user response：

Dictionary comprehensions produce dictionaries, as the name implies. Your code does not produce anything. In fact, it only carries side effects (namely, printing to the console), which should generally be avoided inside of comprehensions.

So the answer is: don't do it.

If you think you still need comprehensions to do this, then my answer is: go to the top of this post and read it again.

Still here? Alright, here's how you force Python to print inside of a comprehension. I cannot stress this enough: This is not good Python code; if I saw this in code review, I'd reject it immediately for multiple reasons.

{ k: print(v) for key, val in new_dict.items() if key == sending_button.text() for k, v in dict_key['printitem'].items() if k == val }

Here are all of the reasons you should not do this.

It carries side effects inside a comprehension
It looks like it produces a dictionary, but that's not the real point of the line; the dictionary is silently discarded
It's a really long single statement of code.
It's written backwards. You have to read the whole line almost right-to-left to figure out what's going on.

In summary: Do not do this