Question

Let’s create a simple tuple, dictionary and function.

>>> tup = (7, 3)
>>> dic = {"kw1":7, "kw2":3}
>>> def pr(a, b):
...    print a, b

The following shows what * does before a tuple and dictionary as an argument.

>>> pr(tup)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: pr() takes exactly 2 arguments (1 given)

>>> pr(*tup)  
7 3   

>>> pr(*dic)
kw1 kw2

Now let’s try ** before an argument.

>>> pr(**tup)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: pr() argument after ** must be a mapping, not tuple

Ok, it seems ** only works when a dictionary is used as an argument. So let’s try it with a dictionary then.

>>> pr(**dic)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: pr() got an unexpected keyword argument 'kw1'

What?
Can anybody show me an example of this last case that doesn’t produce an error?

Answer 1

Your pr function takes arguments a and b, not kw1 and kw2.

>>> def pr(a, b):
...   print a, b
... 
>>> 
>>> d = {'a': 1, 'b':2}
>>> pr(**d)
1 2