import csv
from collections import defaultdict


def get_list(animals_file, toys_file, houses_file):
    """ Join 3 csv files using to a column with name "uid" """ 

    # index will be a dictionary of the form:
    # { uid1:{ "animal":animal1, "toy":toy1, "house":house1 }, uid2:{ ... } }
    index = defaultdict(dict)
    with open(animals_file) as f_animals:
        reader = csv.DictReader(f_animals)
        for row in reader:
            unique_index = int(row["uid"])
            # note that we don't have to check that the dictionary at 'index[unique_index]' already exists as we use defaultdict
            index[unique_index]["animal"] = row["animal"].strip()

    with open(toys_file) as f_toys:
        reader = csv.DictReader(f_toys)
        for row in reader:
            unique_index = int(row["uid"])
            index[unique_index]["toy"] = row["toy"].strip()

    with open(houses_file) as f_houses:
        reader = csv.DictReader(f_houses)
        for row in reader:
            unique_index = int(row["uid"])
            index[unique_index]["house"] = row["house"].strip()

    # we want to return a list instead of a dict, so we remove the indices
    return index.values()

default_template = "the {animal} plays with the {toy} in the {house}"
    
def out_text(mylist, template= default_template, pre="", post=""):
    """ return text from a list of dictionaries according to a template """
    return pre+"\n"+"\n".join(template.format(**my_dict) for my_dict in mylist)+"\n"+post

if __name__ == '__main__':

    my_list = get_list("animals.csv", "toys.csv", "houses.csv")
    print(out_text(my_list))

    table_template = "| {animal:^20} | {toy:^20} | {house:^30} |"
    print(out_text(my_list,table_template,pre="_"*80,post="_"*80))

    html_template = "<tr><td> {animal:^20} </td><td> {toy:^20} </td><td> {house:^30} </td></tr>"
    print(out_text(my_list,html_template,pre="<table>",post="</table>"))