Python：如何将值添加到字典中的现有值

Question

Python 3.6

Hello, writing a program for stock management for school and I can't figure out how to add 1 to an existing number in a dictionary. So I have the quantity of an item stored in a dictionary and can't figure out how to get Python to add 1 to the quantity number. Code is something as shown below:

stock = {'Intel i7-7770T' : ['Intel i7-7770T', '$310', 'New','1101'],
         'Intel i7-7770T QUAN' : [3]}

Would I need to define a function? So if I sell one Intel i7-7770T then "Intel i7-7770T QUAN" should become 2. Or if I get more stock it should become 4. How could I achieve this? Any help would greatly be appreciated. Thank you!

Also the adding is done via a button using Tkinter and I have that figured out. So if this is done via a function I would just link the button to the function.

Answer 1

试试这个：

stock['Intel i7-7770T QUAN'][0] += 1

Answer 2

I would reformat the whole dict:

stock = {
    'Intel i7-7770T': {
        'price_USD': 310,
        'condition': 'New',
        'whatever': '1101',   # should this really be a string, or is it always a number?
        'quantity': 3
    },
    ...
}

Then you can do stuff like stock['Intel i7-7770T']['quantity'] += 1

Other operations should be easier as well. 20 percent discount:

stock['Intel i7-7770T']['price_USD'] *= 0.8

Remove whole item from stock:

stock.pop('Intel i7-7770T')

Answer 3

In a more generalized method than @Danil Speransky with your current dict structure:

def sold(name, quant):
    stock[name + " QUAN"][0] -= quant

---

I would restructure the dict aswell and even consider defining a class to create objects in the dict:

class store_item(object):
    def __init__(self, price, condition, quantity, info1=None, info2=None):
        self.price_usd = price
        self.condition = condition
        self.info1 = info1
        self.info2 = info2
        self.quant = quantity

Then you could make a dict with the objects in it and access it in a nice way (you could even use inheritance to make special classes for different kind of products, for example processors). Example of access:

stock['Intel i7-7770T'].quant -= 1
stock['Intel i7-7770T'].price_usd *= 0.95

Using a class has the advantage, that you can write extra initialization into the object and create methods to do certain actions on the object. For example the discount can be done in a different way that retains the old value:

class store_item(object):
    def __init__(self, price, condition, quantity, discount=None, info1=None, info2=None):
        self.price_usd = price
        self.discount = discount
        self.condition = condition
        self.info1 = info1
        self.info2 = info2
        self.quant = quantity

   def get_price(self, unit):
       if self.discount is None:
           return getattr(self, "price_" + unit)
       else:
           return getattr(self, "price_" + unit) * (1 - self.discount)

Answer 4

There is no need for a list. Just store the quantity as simple value.and just use the value. Your JSON would look like this:

stock = {'Intel i7-7770T' : ['Intel i7-7770T', '$310', 'New','1101'],
     'Intel i7-7770T QUAN' : 3}

And you can access that quantity with stock['Intel i7-7770T QUAN']

Use the code provided in the first two comments to de-/increase the quantity without [0].

And I would recommend to change the structure of the dict and use a dict for the model, price, etc., too. So it's easier and more reliable to refer those attributes by their key then to rely on a list and get them by their index.