Modern Python Standard Library Cookbook

There's more...

Since Python 3.5 through PEP 448, it's now possible to unpack multiple mappings to provide keyword arguments:

>>> def f(a, b, c, d):
...     print (a, b, c, d)
...
>>> d1 = dict(a=5, b=6)
>>> d2 = dict(c=7, d=8)
>>> f(**d1, **d2)
5 6 7 8

This solution is very convenient, but has two limits:

• It's only available in Python 3.5+
• It chokes on duplicated arguments

If you don't know where the mappings/dictionaries you are unpacking come from, it's easy to end up with the issue of duplicated arguments:

>>> d1 = dict(a=5, b=6)
>>> d2 = dict(b=7, c=8, d=9)
>>> f(**d1, **d2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: f() got multiple values for keyword argument 'b'

In the previous example, the b