assign values to list of variables in python

Question

I have made a small demo of a more complex problem

def f(a):
    return tuple([x for x in range(a)])

d = {}
[d['1'],d['2']] = f(2)
print d
# {'1': 0, '2': 1} 
# Works

Now suppose the keys are programmatically generated
How do i achieve the same thing for this case?

n = 10
l = [x for x in range(n)]
[d[x] for x in l] = f(n)
print d
# SyntaxError: can't assign to list comprehension

Note that there is no such thing as a list of variables - [d[x] for x in l] would create a list of the elements of d, which are objects, not variables. Basically, each d[x] doesn't resolve to "x'th position of d" but "object at x'th position of d". The outermost [] in [d['1'], d['2']] mean something different whether they are left or right elements of an assignment. — MisterMiyagi
– MisterMiyagi, Commented Jul 28, 2016 at 8:49

RemcoGerlich · Accepted Answer · 2016-07-28 08:47:51Z

1

You can't, it's a syntactical feature of the assignment statement. If you do something dynamic, it'll use different syntax, and thus not work.

If you have some function results f() and a list of keys keys, you can use zip to create an iterable of keys and results, and loop over them:

d = {}
for key, value in zip(keys, f()):
    d[key] = value

That is easily rewritten as a dict comprehension:

d = {key: value for key, value in zip(keys, f())}

Or, in this specific case as mentioned by @JonClements, even as

d = dict(zip(keys, f()))

answered Jul 28, 2016 at 8:35

RemcoGerlich

31.4k6 gold badges66 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Or... d = dict(zip(keys, f()))