Pandas dataframe from dictionary of list values

Question

I have a dictionary with lists as values such as:

cols = {'animals':['dog','cat','fish'],
        'colors':['red','black','blue','dog']}

I want to convert this into a dataframe in which each of the lists are enumerated according to their key with the result of

key variable
animals dog
animals cat
animal fish
colors red
colors black
colors blue
colors dog

SO far, I have done this: but it does not provide me with desired result.

cols_df = pd.DataFrame.from_dict(cols, orient='index')

How can I modify this to achieve the above?

Answer 1

No imports, works on all inputs:

>>> pd.DataFrame([(key, var) for (key, L) in cols.items() for var in L], 
                 columns=['key', 'variable'])

       key variable
0  animals      dog
1  animals      cat
2  animals     fish
3   colors      red
4   colors    black
5   colors     blue
6   colors      dog