为什么输出为11032？ Python3.6

Question

d = {10:"x", 1:"wx", 2:"yz"}
a = d.setdefault(1)
b = d.setdefault(3)
s = "{}" * len(d)
print(s.format(*d))

Why will the output be 11032?

Answer 1

After 2 setdefault calls,

d = {10: "x", 1: "wx", 2: "yz"}
d.setdefault(1)  # does not change the dictionary because there's already 1
d.setdefault(3)  # add 3 with value None (default if not speicfied)

d becomes:

>>> d
{10: 'x', 1: 'wx', 2: 'yz', 3: None}

Iterating dictionary yields dictionary keys: 10, 1, 2, 3 . (iteration performed by *d to unpack the argument d ):

>>> for key in d:
...     print(key)
... 
10
1
2
3

So, s.format(*d) is equivalent to '{}{}{}{}'.format(10, 1, 2, 3) .