CODEWITHSUNDEEP
python
Robert
Robert

Reputation: 71

__init__() missing 1 required positional argument: 'b'

Here is two vectors :

a = [1, 2, 3, 4, 5, 6, 7, 8]
b = [3, 4, 5, 6, 7, 8, 9, 10]

Suppose I define Test class this way :

class Test:
   def __init__(self, a, b):
      self.a = a
      self.b = b

When I execute the command list(map(Test, zip(a,b))), it says __init__() missing 1 required positional argument: 'b'. I know if I have t = (1,2), then I can create an instance of Test with inst = Test(*t). Can I apply * to solve my problem using map? Is there a workaround?

Upvotes: 0

Views: 480

Answers (1)

rdas
rdas

Reputation: 21295

Yes. You can do this:

tests = list(map(lambda args: Test(*args), zip(a,b)))

Which takes the zip values as argument to a lambda & unwraps them when calling Test()

This is pretty much what itertools.starmap does - so that's another option:

tests = list(starmap(Test, zip(a,b)))

The better option is to use a list-comprehension which makes the code much more readable:

tests = [Test(arg_a, arg_b) for (arg_a,arg_b) in zip(a, b)]

Upvotes: 2

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