从给定字符开始的给定长度的字符列表中创建所有可能的单词

Question

I need to create all the possible word list from a list of characters for a given length that starts with a given character.

Eg:

char_list = a,b,c
min_len = 2
max_len = 3

Update:

start with = c

so the fucntion should return something like this:

ca, cb, cc, cab, cac, cba, cbc...

How would I do this in python? Your help will be very much appreciated. Thank you.

Answer 1

You create a product object using the itertools.product class from the standard library

import itertools

[''.join(i) for i in itertools.product(char_list, repeat= 2) if i[0].startswith('c')]
['ca', 'cb', 'cc']

[''.join(i) for i in itertools.product(char_list, repeat=3) if i[0].startswith('c')]
['caa', 'cab', 'cac', 'cba', 'cbb', 'cbc', 'cca', 'ccb', 'ccc']

To generate a word list for range of numbers use a generator function

def generate_word(chars_list, my_char, min_len, max_len):
    for i in range(min_len, max_len+1):
        for j in itertools.product(chars_list, repeat=i):
            if j[0].startswith(my_char):
                yield ''.join(j)

for word in generate_word(char_list, 'c', 2, 4):   
    print(word)

Output

ca
cb
cc
caa
cab
cac
cba
cbb
cbc
cca
ccb
ccc
caaa
caab
caac
caba
cabb
cabc
caca
cacb
cacc
cbaa
cbab
....

Answer 2

Here's a program that uses a similar technique to Eithos's code. It creates a generator so you can get the words one at a time, if you want. The generator code will work on Python 2.6, and later, but you'll need to change the print for Python 3.

#!/usr/bin/env python

import itertools

def word_generator(chars, start_with, min_len, max_len):
    for i in range(min_len - 1, max_len):
        for s in itertools.product(chars, repeat=i):
            yield start_with + ''.join(s)    

for word in word_generator('abc', 'c', 2, 4):
    print word

output

ca
cb
cc
caa
cab
cac
cba
cbb
cbc
cca
ccb
ccc
caaa
caab
caac
caba
cabb
cabc
caca
cacb
cacc
cbaa
cbab
cbac
cbba
cbbb
cbbc
cbca
cbcb
cbcc
ccaa
ccab
ccac
ccba
ccbb
ccbc
ccca
cccb
cccc

If you want the words in a list rather than one at a time, you can do:

word_list = list(word_generator('abc', 'c', 2, 4))

Answer 3

This will do exactly what you want, I think:

I made a mistake earlier when I thought itertools.combinations_with_replacement would do the trick. Michael's post (which originally used permutations ) made me reflect on my choice, so I started re-working the code. I actually got it working, but I quickly realized it was not the right tool for the job. Then I realized what you really needed is itertools.product

from itertools import product

minLen = 4
maxLen = 8
sChar = 'a'
print [sChar + ''.join(i) for x in range(minLen-1, maxLen) 
    for i in product(['a','b','c'], repeat=x)]

But if you try a smaller input to test:

minLen = 2
maxLen = 3

you get:

['aa', 'ab', 'ac', 'aaa', 'aab', 'aac', 'aba', 'abb', 'abc', 'aca', 'acb', 'acc']

We can also use c (per the updated post):

minLen = 2
maxLen = 3
sChar = 'c'

['ca', 'cb', 'cc', 'caa', 'cab', 'cac', 'cba', 'cbb', 'cbc', 'cca', 'ccb', 'ccc']