How can I pass a defined dictionary to **kwargs in Python?

Question

I learned how to pass both **kwargs and *args into a function, and it worked pretty well, like the following:

def market_prices(name, **kwargs):
     print("Hello! Welcome to "+name+" Market!")
     for fruit, price in kwargs.items():
         price_list = " {} is NTD {} per piece.".format(fruit,price)
         print (price_list) 
market_prices('Wellcome',banana=8, apple=10)

However in real case, I'd rather pre-defined a dictionary with lots of key&value, so I won't don't have to type in every parameter when calling my function. I have searched online but cannot find a good example or explanation: Here is the code I try to utilize:

fruits:{"apple":10,
       "banana":8,
       "pineapple":50,
       "mango":45
       }

def market_prices(name, **fruits):
    print("Hello! Welcome to "+name+" Market!")
    for fruit, price in fruits.items():
        price_list = " {} is NTD {} per piece.".format(fruit,price)
        print (price_list)

>>> market_prices('Wellcome ', fruits)

NameError: name 'fruits' is not defined

Solution 1

There are 4 possible cases:

You call the function using named arguments and you want named variables in the function:
(note the default values)

def buy(orange=2, apple=3):
    print('orange: ', orange)
    print('apple: ', apple)

buy(apple=4)
# orange:  2
# apple:  4

You call the function using named arguments but you want a dictionary in the function:
then use **dictionaryname in the function definition to collect the passed arguments

def buy(**shoppinglist):
    for name, qty in shoppinglist.items():
        print('{}: {}'.format(name, qty) )

buy(apple=4, banana=5)
# banana: 5
# apple: 4

You call the function passing a dictionary but you want named variables in the function:
use **dictionaryname when calling the function to unpack the dictionary

def buy(icecream=1, apple=3, egg=1):
    print('icecream:', icecream)
    print('apple:', apple)
    print('egg:', egg)

shoppinglist = {'icecream':5, 'apple':1}
buy(**shoppinglist)
# icecream: 5
# apple: 1
# egg: 1

You call the function passing a dictionary and you want a dictionary in the function:
just pass the dictionary

def buy(shoppinglist):
    for name, qty in shoppinglist.items():
        print('{}: {}'.format(name, qty) )

shoppinglist = {'egg':45, 'apple':1}
buy(shoppinglist)
# egg: 45
# apple: 1

Solution 2

Use ** before fruits argument.

fruits={"apple":10,
       "banana":8,
       "pineapple":50,
       "mango":45
       }

def market_prices(name, **fruits):
    print("Hello! Welcome to "+name+" Market!")
    for fruit, price in fruits.items():
        price_list = " {} is NTD {} per piece.".format(fruit,price)
        print (price_list)

market_prices('Wellcome ', **fruits) #Use **before arguments

Solution 3

You have a typo defining fruits. It should have been like the following

fruits = {"apple":10,
       "banana":8,
       "pineapple":50,
       "mango":45
       }

Solution 4

Acknowledgments to you guys for the quick and useful comments!

While defining a function, if you put ** for your argument, then make sure to put it too when calling it! Otherwise, put neither!

1. With **

   fruits={"apple":10,
          "banana":8,
          "pineapple":50,
          "mango":45
          }
   
       def market_prices(name, **fruits):
           print("Hello! Welcome to "+name+" Market!")
           for fruit, price in fruits.items():
               price_list = " {} is NTD {} per piece.".format(fruit,price)
               print (price_list)
   
       market_prices('Wellcome ', **fruits)
   

2. Without **

   fruits={"apple":10,
          "banana":8,
          "pineapple":50,
          "mango":45
          }
   
       def market_prices(name, fruits):
           print("Hello! Welcome to "+name+" Market!")
           for fruit, price in fruits.items():
               price_list = " {} is NTD {} per piece.".format(fruit,price)
               print (price_list)
   
       market_prices('Wellcome ', fruits)
   

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Comments

[chepner]

Note that prior to Python 3.6, this would have shown up as a syntax error. Now, it's just an odd-looking variable annotation.

[Pedro A. Aranda]

Just for the sake of completeness, in most cases you will see something like def market_place(name,**kwargs): that you use like market_place('La Cebada',**fruits) (PS: La Cebada is one of the historical markets in Madrid ;-) )