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 combine 2 dictionaries into a third, and the above expression does an excellent job. I'm interested in the ** operator and what exactly does it do with the expression. I thought ** was a power operator and had not yet seen him in the context above.

Full code snippet:

 >>> 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 the argument lists is of particular importance, as described in the section of section 4.7 of the textbook . The dictionary (or dictionary-like) object passed with **kwargs is expanded into the keyword arguments to the called one, just as *args decomposed into separate positional arguments.

Answer 2

** translation of the dictionary into keywords:

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

becomes:

 >>> d3 = dict(d1, c=3, d=4) 

Answer 3

In Python, any function can take multiple arguments with *; or multiple keyword arguments with **.

An example of a receiving side:

 >>> def fn(**kwargs): ... for kwarg in kwargs: ... print kwarg ... >>> fn(a=1,b=2,c=3) a c b 

Call side example (thanks to Thomas):

 >>> mydict = dict(a=1,b=2,c=3) >>> fn(**mydict) a c b 

Answer 4

Also worth mentioning is the mechanics of the dict constructor. It takes the initial dictionary as the first argument and can also accept keyword arguments, each of which represents a new member to be added to the newly created dictionary.

Answer 5

This statement is used to unpack the argument list: http://docs.python.org/tutorial/controlflow.html#unpacking-argument-lists

Answer 6

you have operator response **. here is another way to add dictionaries

 >>> d1 = {'a': 1, 'b': 2} >>> d2 = {'c': 3, 'd': 4} >>> d3=d1.copy() >>> d3.update(d2) >>> d3 {'a': 1, 'c': 3, 'b': 2, 'd': 4}