What is the difference between **kwargs and dict in Python 3.2?

Question

It seems that many aspects of python are just duplicates of functionality. Is there some difference beyond the redundancy I am seeing in kwargs and dict within Python?

Answer 1

There is a difference in argument unpacking (where many people use kwargs) and passing dict as one of the arguments:

• Using argument unpacking:

  # Prepare function
  def test(**kwargs):
      return kwargs
  
  # Invoke function
  >>> test(a=10, b=20)
  {'a':10,'b':20}
  

• Passing a dict as an argument:

  # Prepare function
  def test(my_dict):
      return my_dict
  
  # Invoke function
  >>> test(dict(a=10, b=20))
  {'a':10,'b':20}
  

The differences are mostly:

• readability (you can simply pass keyword arguments even if they weren't explicitly defined),
• flexibility (you can support some keyword arguments explicitly and the rest using **kwargs),
• argument unpacking helps you avoid unexpected changes to the object "containing" the arguments (which is less important, as Python in general assumes developers know what they are doing, which is a different topic),

Answer 2

It is right that in most cases you can just interchange dicts and **kwargs.

For example:

my_dict = {'a': 5, 'b': 6}
def printer1(adict):
    return adict
def printer2(**kwargs):
    return kwargs

#evaluate:
>>> printer1(my_dict)
{'a': 5, 'b': 6}
>>> printer2(**my_dict)
{'a': 5, 'b': 6}

However with kwargs you have more flexibility if you combine it with other arguments:

def printer3(a, b=0, **kwargs):
    return a,b,kwargs

#evaluate
>>> printer3(**my_dict)
(5, 6, {})