Minecraft calculator

craft.py

import json
import sys
import math
from fractions import Fraction

def craft(item, number, recipes, L=None):
    if L != None and L <= 0:
        return {item: number}
    if item not in recipes:
        return {item: number}
    # otherwise, do the recursion
    out = {}
    recipe = recipes[item]
    for ingredient, n in recipe.items():
        if L != None:
            result = craft(ingredient, n*number, recipes, L-1)
        else:
            result = craft(ingredient, n*number, recipes)
        for item, m in result.items():
            if item in out:
                out[item] += m
            else:
                out[item] = m
    return out

def printnice(result):
    for ingredient, n in result.items():
        print("{0:>5} {1}".format(math.ceil(n), ingredient))

def loadRecipes(filename):
    with open(filename) as f:
        recipes = json.load(f)
    for item in recipes:
        recipe = recipes[item]
        editlist = []
        for ingredient, n in recipe.items():
            if type(n) == str:
                editlist.append((ingredient, n))
        for ingredient, n in editlist:
            recipe[ingredient] = Fraction(n)
    return recipes

if __name__=="__main__":
    recipes = loadRecipes("items.json")
    itemname = sys.argv[1]
    printnice(craft(itemname, 1, recipes))

items.json

{
	"reinforced hull": {
		"reinforced metal": 5,
		"reinforced wheels": 2
	},
	"reinforced wheels": {
		"iron ingot": 4,
		"reinforced metal": 1
	},
	"reinforced metal": {
		"iron ingot": 1,
		"hardened mesh": "1/5",
		"refined hardener": "3/5"
	},
	"refined hardener": {
		"obsidian": 2,
		"diamond": "1/2"
	},
	"hardened mesh": {
		"iron bars": 5,
		"refined hardener": 4
	},
	"iron bars": {
		"iron ingot": "6/16"
	},
	"conductive iron": {
		"iron ingot": 1,
		"redstone dust": 1
	},
	"leather strap": {
		"iron ingot": 2,
		"leather": 4
	},
	"basic capacitor": {
		"copper ingot": 1,
		"redstone": 4,
		"gold nugget": 2
	},
	"conductive iron thruster": {
		"conductive iron": 2,
		"basic capacitor": 2,
		"basic gear": 2,
		"insulated redstone conduit": 2
	},
	"basic gear": {
		"cobblestone": 4,
		"stick": 4
	},
	"insulated redstone conduit": {
		"redstone alloy": 3,
		"conduit binder": 6
	},
	"redstone alloy": {
		"redstone dust": 1,
		"silicon": 1
	},
	"conductive iron jetpack": {
		"conductive iron": 4,
		"leather strap": 1,
		"basic capacitor": 1,
		"conductive iron thruster": 2
	},
	"electrical steel jetpack": {
		"electrical steel": 4,
		"basic capacitor": 1,
		"electrical steel thruster": 2,
		"conductive iron jetpack": 1
	},
	"electrical steel thruster": {
		"electrical steel": 2,
		"energy conduit": 2,
		"machine chassis": 2,
		"redstone dust": 1,
		"basic capacitor": 2
	},
	"machine chassis": {
		"iron bars": 4,
		"iron ingot": 4,
		"basic capacitor": 1
	},
	"electrical steel": {
		"iron ingot": 1,
		"coal": 1,
		"silicon": 1
	}
}