一旦到达 python 代码中的最后一个字母，如何打破这个递归循环？

Question

I would like to break the recursive loop once I reach the last letter of new. How can I do this?

Diction is a dictionary. The idea here is that I get a word there is an example below and I shrink it by matching the [i:i+1] positions of the word string with the dictionary until it gets down to one letter.

def eval(word):
    diction = {
        'br': 'y',
        'rb': 'y',
        'by': 'r',
        'yb': 'r',
        'yr': 'b',
        'ry': 'b',
        'bb': 'b',
        'yy': 'y',
        'rr': 'r',
    }
    new = ''
    i = 0
    while i < len(word) - 1:
        key1 = word[i:i + 2]
        i += 1
        new += diction[key1]
    return eval(new)


word = 'brybbr'
print(eval(word))

Answer 1

You need to provide the end condition.

In this code, I added a condition if len(new)==1: to finish the unlimited resursive calls.

In addition, I also added print(new) inside the eval() instead print(eval(word)) so that it can print new with each calling of eval() .

def eval(word):
    diction = {
        'br': 'y',
        'rb': 'y',
        'by': 'r',
        'yb': 'r',
        'yr': 'b',
        'ry': 'b',
        'bb': 'b',
        'yy': 'y',
        'rr': 'r',
    }
    new = ''
    i = 0
    while i < (len(word) - 1):
        key1 = word[i:i + 2]
        i += 1
        new += diction[key1]
    print(new) # to print new for every `eval()` calling.
    if len(new)==1: # to stop endless resursive calling.
        return None
    else:
        return eval(new)


word = 'brybbr'
eval(word)
# ybrby
# ryyr
# byb
# rr
# r
#