使用字典替换文本中的单词

Question

I am trying to create a program that replaces word from a string.

ColorPairs = {'red':'blue','blue':'red'}

def ColorSwap(text):
    for key in ColorPairs:
        text = text.replace(key, ColorPairs[key])
    print text

ColorSwap('The red and blue ball')
# 'The blue and blue ball'
instead of
# 'The blue and red ball'

This program replaces 'red' to 'blue', but not 'blue' to 'red'.I am stuck trying to figure out a way to make it so that the program doesn't override the first replaced key.

Answer 1

You could use re.sub function.

import re
ColorPairs = {'red':'blue','blue':'red'}
def ColorSwap(text):
    print(re.sub(r'\S+', lambda m: ColorPairs.get(m.group(), m.group()) , text))

ColorSwap('The blue red ball')

\\S+ matches one or more non-space characters. You could use \\w+ instead of \\S+ also. Here for each single match, python would check for the match against the dictionary key. If there is a key like the match then it would replace the key in the string with the value of that particular key.

If there is no key found, it would display KeyError if you use ColorPairs[m.group()] . So that i used dict.get() method which returns a default value if there is no key found.

Output:

The red blue ball

Answer 2

Since the dictionary is unordered, So It may take blue converted to red in the first iteration and in the second iteration it change again from red to blue . So in order to get the result you need to code in this manner. This is certainly not the best Solution but an alternate way.

import re
def ColorSwap(text):
    text = re.sub('\sred\s',' blue_temp ', text)
    text = re.sub('\sblue\s', ' red_temp ', text)
    text = re.sub('_temp','', text)
    return text

print ColorSwap('The red and blue ball')

Answer 3

If you don't want to use regex as suggested by @Avinash, you can split text into words, replace and then join.

ColorPairs = {'red':'blue','blue':'red'}
def ColorSwap(text):
    textList = text.split(' ')
    text = ' '.join(ColorPairs.get(k, k) for k in textList)
    print text

ColorSwap('The red and blue ball')

output

The blue and red ball