pythonargument-unpacking

Why do I need '**' when loading json (Python)

t1 = Tournament("Aeroflot Open", 2010)
json_data = json.dumps(t1.__dict__)
print(json_data)

t = Tournament(**json.loads(json_data)) # <-------------------
print(f"name = {t.name}, year = {t.year}")

Could someone explain me why do I need these two asterisks ** when loading the json back. The line is above.

Solution

  • In Python, there is unpacking of the iterator using * and unpacking of the dictionary using **.

    Let's understand it with examples.

    
# here is the class
class Tournament:

  def __init__(self, name, age):
     self.name = name
     self.year = year 

# here is init data in your case json.loads will
data = {
  "name": "IPL",
  "year": 13
}

    python will assign the key as a argument name and value as argument value like {"name": "IPL", "year": 13} the Tournament(name="IPL", year=13)

    tournament = Tournament(**data)
print(f"name = {tournament.name}, year = {tournament.year}")

    Either you can directly assign the data, like

    tournament = Tournament(name="IPL", year=13)
print(f"name = {tournament.name}, year = {tournament.year}")

    For more understanding, follow this * and **