python - __init__() missing 1 required positional argument

30

votes

I am trying to learn Python. This is a really simple code. All I am trying to do here is to call a class's constructor. Initialize some variables there and print that variable. But it is giving me an error. It is saying:

missing 1 required positional argument

Here is my code:

class DHT:
    def __init__(self, data):
        self.data['one'] = '1'
        self.data['two'] = '2'
        self.data['three'] = '3'
    def showData(self):
        print(self.data)

if __name__ == '__main__': DHT().showData()

pythonpython-3.xconstructor

16

votes

You're receiving this error because you did not pass a data variable to the DHT constructor.

aIKid and Alexander's answers are nice but it wont work because you still have to initialize self.data in the class constructor like this:

class DHT:
   def __init__(self, data=None):
      if data is None:
         data = {}
      else:
         self.data = data
      self.data['one'] = '1'
      self.data['two'] = '2'
      self.data['three'] = '3'
   def showData(self):
      print(self.data)

And then calling the method showData like this:

DHT().showData()

Or like this:

DHT({'six':6,'seven':'7'}).showData()

or like this:

# Build the class first
dht = DHT({'six':6,'seven':'7'})
# The call whatever method you want (In our case only 1 method available)
dht.showData()

4

votes

Your constructor is expecting one parameter (data). You're not passing it in the call. I guess you wanted to initialise a field in the object. That would look like this:

class DHT:
    def __init__(self):
        self.data = {}
        self.data['one'] = '1'
        self.data['two'] = '2'
        self.data['three'] = '3'
    def showData(self):
        print(self.data)

if __name__ == '__main__':
    DHT().showData()

Or even just:

class DHT:
    def __init__(self):
        self.data = {'one': '1', 'two': '2', 'three': '3'}
    def showData(self):
        print(self.data)

2

votes

You should possibly make data a keyword parameter with a default value of empty dictionary:

class DHT:
    def __init__(self, data=dict()):
        self.data['one'] = '1'
        self.data['two'] = '2'
        self.data['three'] = '3'
    def showData(self):
        print(self.data)

if __name__ == '__main__': 
    DHT().showData()

1

votes

You need to pass some data into it. An empty dictionary, for example.

if __name__ == '__main__': DHT('a').showData()

However, in your example a parameter is not even needed. You can declare it by just:

def __init__(self):

Maybe you mean to set it from the data?

class DHT:
    def __init__(self, data):
        self.data['one'] = data['one']
        self.data['two'] = data['two']
        self.data['three'] = data['three']
    def showData(self):
        print(self.data)

if __name__ == '__main__': DHT({'one':2, 'two':4, 'three':5}).showData()

showData will print the data you just entered.

0

votes

The problem is with, you

def __init__(self, data):

when you create object from DHT class you should pass parameter the data should be dict type, like

data={'one':1,'two':2,'three':3}
dhtObj=DHT(data)

But in your code youshould to change is

data={'one':1,'two':2,'three':3}
if __name__ == '__main__': DHT(data).showData()

Or

if __name__ == '__main__': DHT({'one':1,'two':2,'three':3}).showData()

0

votes

If error is like Author=models.ForeignKey(User, related_names='blog_posts') TypeError:init() missing 1 required positional argument:'on_delete'

Then the solution will be like, you have to add one argument Author=models.ForeignKey(User, related_names='blog_posts', on_delete=models.DO_NOTHING)

python - init() missing 1 required positional argument

6 Answers