Problems

currency.py

def convert(graph, start, end, path=None):
    if path is None:
        path = []

    if start == end:
        return 1

    for child in graph:
        if child[0] == start and child[0] not in path:
            result = convert(graph, child[1], end, path + [child[0]])
            if result != 0:
                return child[2] * result
        elif child[1] == start and child[1] not in path:
            result = convert(graph, child[0], end, path + [child[1]])
            if result != 0:
                return (1 / child[2]) * result

    return 0


if __name__ == '__main__':
    currencies = [
        ('BGN', 'EUR', 0.51),
        ('EUR', 'GBP', 0.87),
        ('USD', 'GBP', 0.72),
        ('CAD', 'BGN', 1.30),
    ]

    print(convert(currencies, 'BGN', 'USD')) # 0.61625
    print(convert(currencies, 'GBP', 'BGN')) # 2.25377
    print(convert(currencies, 'USD', 'CAD')) # 1.24824