Unpacking generator which yields a dictionary

Question

I cannot understand the output of the following sample code:

def g1():
    d = {'a':1, 'b':2, 'c':3}
    yield d

for a,b,c in g1():
    print a,b,c

In Python 2.7.14, the above would print out

a c b

There are two interesting aspects of this behavior:

1. That it prints out acb intead of the sorted abc , which is supposed to be the case since we are talking about dictionary keys.
2. If you just define the dictionary without writing the generator d = {'a':1, 'b':2, 'c':3} , and then for a,b,c in d: , this will be a valueError.

Answer 1

First point: dicts simply aren't ordered in Python 2.7. Don't rely on it until 3.7+.

Second point: The generator g1() , when iterated , yielded a dictionary. The proposed alternative:

for a,b,c in d:
    ...

is apples to oranges, this is iterating the dictionary itself. For an equivalent duck to unpack here, you'll need an object which returns a dictionary when iterated :

for a,b,c in [d]:
    ...

Answer 2

1.) In Python 2.7, dictionaries are unordered.

2.) for a,b,c in d: will give you an error because you're trying to unpack just the keys of the dictionary into three variables, which won't work. You could however do for a, b in d.items() as it returns a list of tuple pairs.

Answer 3

Colin's answer pretty much answer your questions. But if you want to solve your first problem with unordered list, try using built in class OrderedDict under collections library.