Dictionary Comprehension in Python 3
python, python-3.x
Solution
Looping over a dictionary only yields the keys. Use `d.items()` to loop over both keys and values:
{key: value for key, value in d.items()}
The `ValueError` exception you see is not a dict comprehension problem, nor is it limited to Python 3; you'd see the same problem in Python 2 or with a regular `for` loop:
>>> d = {'a':1, 'b':2, 'c':3, 'd':4}
>>> for key, value in d:
... print key, value
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: need more than 1 value to unpack
because each iteration there is only one item being yielded.
Without a transformation, `{k: v for k, v in d.items()}` is just a verbose and costly `d.copy()`; use a dict comprehension only when you do a little more with the keys or values, or use conditions or a more complex loop construct.
Problem
I found the following stack overflow post about dict comprehensions in `Python2.7` and `Python 3+`: Create a dictionary with list comprehension in Python stating that I can apply dictionary comprehensions like this: ``` d = {key: value for (key, value) in sequence} ``` I tried it in Python 3. However, it raises an exception. ``` d = {'a':1, 'b':2, 'c':3, 'd':4} {key : value for (key, value) in d} {key : value for key, value in d} ``` Both versions raise a `ValueError` saying that `ValueError: need more than 1 value to unpack`. What is the easiest / the most direct way to make a dictionary comprehension in Python3?