Help_the_bookseller.py

# Kata link:
# https://www.codewars.com/kata/54dc6f5a224c26032800005c/train/python

# -------------------------------------
# Instructions:
'''
A bookseller has lots of books classified in 26 categories labeled A, B, ... Z. Each book has a code c of 3, 4, 5 or more characters. The 1st character of a code is a capital letter which defines the book category.

In the bookseller's stocklist each code c is followed by a space and by a positive integer n (int n >= 0) which indicates the quantity of books of this code in stock.

For example an extract of a stocklist could be:

        L = {"ABART 20", "CDXEF 50", "BKWRK 25", "BTSQZ 89", "DRTYM 60"}.
        or
        L = ["ABART 20", "CDXEF 50", "BKWRK 25", "BTSQZ 89", "DRTYM 60"] or ....

You will be given a stocklist (e.g. : L) and a list of categories in capital letters e.g :

        M = {"A", "B", "C", "W"} 
        or
        M = ["A", "B", "C", "W"] or ...

and your task is to find all the books of L with codes belonging to each category of M and to sum their quantity according to each category.

For the lists L and M of example you have to return the string:

        (A : 20) - (B : 114) - (C : 50) - (W : 0)

where A, B, C, W are the categories, 20 is the sum of the unique book of category A, 114 the sum corresponding to "BKWRK" and "BTSQZ", 50 corresponding to "CDXEF" and 0 to category 'W' since there are no code beginning with W.

If L or M are empty return string is "" (Clojure and Racket should return an empty array/list instead).

Note:
In the result codes and their values are in the same order as in M.
'''

# -------------------------------------
# Solution:

def stock_list(listOfArt, listOfCat):
    M = {key: 0 for key in listOfCat}
    for item in listOfArt:
        if item[0] in listOfCat:
            value = int(item[item.find(" "):])
            M[item[0]] += value
    if sum(M.values()) == 0:
        return ''
    else:
        return " - ".join([f"({k} : {v})" for k, v in M.items()])

# Basic Tests
b = ["ABAR 200", "CDXE 500", "BKWR 250", "BTSQ 890", "DRTY 600"]
c = ["A", "B"]
print(stock_list(b, c)," = ", "(A : 200) - (B : 1140)")