如何将两个列表的所有组合拆分N次？

Question

Pardon if the question is titled confusingly. I couldn't think of a better way to word it. Anyway, I have a Python program that accepts a list of first names and a list of last names. It then "splits" the two into all of their combinations, with a maximum of 5 results. The code explains it better:

def getLists(firstNames, lastNames, resultCount):
    firstNameCount = len(firstNames)
    lastNameCount = len(lastNames)

    if firstNameCount >= resultCount:
        # Return the last name list as is.
        return [firstNames[i * firstNameCount / resultCount:(i + 1) * firstNameCount / resultCount] for i in xrange(resultCount)], [lastNames for _ in xrange(resultCount)]

    else:
        lastNameLists = []
        firstNameLists = [[firstNames[i % firstNameCount]] for i in xrange(resultCount)]

        for i in xrange(resultCount):
            firstName = firstNameLists[i]
            total = firstNameLists.count(firstName)
            already = total - firstNameLists[i:].count(firstName)
            lastNameLists.append(lastNames[already * lastNameCount / total:(already + 1) * lastNameCount / total])

        # Return the last names, split depending on how many results and first names.
        return firstNameLists, lastNameLists

If there are less first names than the maximum (5), the first names are repeated until the maximum and the last names are distributed among the first names:

firstNames = ['firstName{}'.format(i) for i in xrange(1, 3)]
lastNames = ['lastName{}'.format(i) for i in xrange(1, 8)]
comboCount = len(firstNames) * len(lastNames)
resultCount = min(comboCount, 5)
firstNameLists, lastNameLists = getLists(firstNames, lastNames, resultCount)

for i in xrange(resultCount):
    print 'Result #{}:\nFirst Names: {}\nLast Names: {}'.format(i + 1, firstNameLists[i], lastNameLists[i])
    print

Output:

Result #1:
First Names: ['firstName1']
Last Names: ['lastName1', 'lastName2']

Result #2:
First Names: ['firstName2']
Last Names: ['lastName1', 'lastName2', 'lastName3']

Result #3:
First Names: ['firstName1']
Last Names: ['lastName3', 'lastName4']

Result #4:
First Names: ['firstName2']
Last Names: ['lastName4', 'lastName5', 'lastName6', 'lastName7']

Result #5:
First Names: ['firstName1']
Last Names: ['lastName5', 'lastName6', 'lastName7']

If there are more first names than the maximum (5), the first names are distributed as evenly as possible and the last names are copied for each:

firstNames = ['firstName{}'.format(i) for i in xrange(1, 8)]
lastNames = ['lastName{}'.format(i) for i in xrange(1, 8)]
comboCount = len(firstNames) * len(lastNames)
resultCount = min(comboCount, 5)
firstNameLists, lastNameLists = getLists(firstNames, lastNames, resultCount)

for i in xrange(resultCount):
    print 'Result #{}:\nFirst Names: {}\nLast Names: {}'.format(i + 1, firstNameLists[i], lastNameLists[i])
    print

Output:

Result #1:
First Names: ['firstName1']
Last Names: ['lastName1', 'lastName2', 'lastName3', 'lastName4', 'lastName5', 'lastName6', 'lastName7']

Result #2:
First Names: ['firstName2']
Last Names: ['lastName1', 'lastName2', 'lastName3', 'lastName4', 'lastName5', 'lastName6', 'lastName7']

Result #3:
First Names: ['firstName3', 'firstName4']
Last Names: ['lastName1', 'lastName2', 'lastName3', 'lastName4', 'lastName5', 'lastName6', 'lastName7']

Result #4:
First Names: ['firstName5']
Last Names: ['lastName1', 'lastName2', 'lastName3', 'lastName4', 'lastName5', 'lastName6', 'lastName7']

Result #5:
First Names: ['firstName6', 'firstName7']
Last Names: ['lastName1', 'lastName2', 'lastName3', 'lastName4', 'lastName5', 'lastName6', 'lastName7']

How could I make getLists more efficient, readable, and/or cleaner?

Answer 1

The demo is Python3, if you use Python2, try to make a little code change if possible:

firstNames = ['firstName{}'.format(i) for i in range(1, 3)]
lastNames = ['lastName{}'.format(i) for i in range(1, 2)]

from itertools import product, islice

print(list(islice(product(firstNames, lastNames), 5)))

the islice ensure it returns the first 5 result, if the results is less than 5, it's still OK.