从两个大小不同的列表中创建一个列表（元组？）

Question

I am stuck trying to perform this task and while trying I can't help thinking there will be a nicer way to code it than the way I have been trying.

I have a line of text and a keyword. I want to make a new list going down each character in each list. The keyword will just repeat itself until the end of the list. If there are any non-alpha characters the keyword letter will not be used.

For example:

Keyword="lemon"
Text="hi there!"

would result in

('lh', 'ei', ' ', 'mt' , 'oh', 'ne', 'lr', 'ee', '!')

Is there a way of telling python to keep repeating over a string in a loop, ie keep repeating over the letters of lemon?

I am new to coding so sorry if this isn't explained well or seems strange!

Answer 1

You've got two questions mashed into one. The first is: how do you remove non-alphanumeric chars from a string? You can do it a few ways, but regular expression substitution is a nice way.

import re

def removeWhitespace( s ):
    return re.sub( '\s', '', s )

The second part of the question is about how to keep looping through the keyword, until the text line is consumed. You can write this as:

def characterZip( keyword, textline ):
    res = []
    textline = removeWhitespace(textline)
    textlen = len(textline)
    for i in xrange(textlen)):
        res.append( '%s%s' % (keyword[i%len(keyword)], textline[i]) )
    return res

Most pythonistas will look at this and see opportunity for refactoring. The patten that this code is trying to achieve is in functional programming termed a zip . The quirk is that in this case you're doing something slightly non-normative with the repeating characters of the keyword, this too has an equivalent, the cycle function in the itertools module.

from itertools import cycle, islice, izip

def characterZip( keyword, textline ):
    textline = removeWhitespace(textline)
    textlen = len(textline)
    it = islice( izip(cycle(keyword), textline), textlen )
    return [ '%s%s' % val for val in it ]

Answer 2

Here's a solution:

import itertools

def task(kw,text):
    i = itertools.cycle(kw)
    return tuple(next(i)+t if t.isalpha() else t for t in text)

print(task('lemon','hi there!'))

Output

('lh', 'ei', ' ', 'mt', 'oh', 'ne', 'lr', 'ee', '!')

itertools.cycle iterates over a sequence repeatedly (a string is a sequence of characters). next gets the next character from the repeating sequence. The generator expression selects the pair of next keyword letter and text character if the text character is alphabetic, else it just selects the non-alphabetic character alone.

Answer 3

I think you could use enumerate in that situation:

# remove unwanted stuff
l = [ c for c in Text if c.isalpha() ]

for n,k in enumerate(l):
   print n, (Keyword[n % len(Keyword)], Text[l])

that gives you:

0 ('l', 'h')
1 ('e', 'i')
2 ('m', 't')
3 ('o', 'h')
4 ('n', 'e')
5 ('l', 'r')
6 ('e', 'e')

You could use that as the basis for your manipulation.