If you don't care about the order of your columns (since dictionaries are unordered), you can simply use zip()
:
d = {"key1": [1,2,3], "key2": [4,5,6], "key3": [7,8,9]}
with open("test.csv", "wb") as outfile:
writer = csv.writer(outfile)
writer.writerow(d.keys())
writer.writerows(zip(*d.values()))
Result:
key3 key2 key1
7 4 1
8 5 2
9 6 3
If you do care about order, you need to sort the keys:
keys = sorted(d.keys())
with open("test.csv", "wb") as outfile:
writer = csv.writer(outfile, delimiter = "\t")
writer.writerow(keys)
writer.writerows(zip(*[d[key] for key in keys]))
Result:
key1 key2 key3
1 4 7
2 5 8
3 6 9