python - What does `**` mean in the expression `dict(d1, **d2)`?

Question

I am intrigued by the following python expression:

d3 = dict(d1, **d2)

The task is to merge 2 dictionaries into a third one, and the above expression accomplishes the task just fine. I am interested in the ** operator and what exactly is it doing to the expression. I thought that ** was the power operator and haven't seen it used in the context above yet.

The full snippet of code is this:

>>> d1 = {'a': 1, 'b': 2}
>>> d2 = {'c': 3, 'd': 4}
>>> d3 = dict(d1, **d2)
>>> print d3
{'a': 1, 'c': 3, 'b': 2, 'd': 4}

Answer 1

** in argument lists has a special meaning, as covered in section 4.7 of the tutorial. The dictionary (or dictionary-like) object passed with **kwargs is expanded into keyword arguments to the callable, much like *args is expanded into separate positional arguments.