如何查找字符串中所有要求的字符或组合

Question

I want insert some text and find in this text some selected characters with index in sequence for each letter, for example

all letters L and O in "hello world!"

Answer 1

If you want the index for each characters use a defaultdict where the keys are the letters and the values are lists containing the index/indexes where that letter appears, you can get the index of each character using enumerate :

s = "hello world!"

from collections import defaultdict
d = defaultdict(list)


for ind, ch in enumerate(s):
    d[ch].append(ind)

Then to find the index lookup using the letter:

In [46]: d["o"]
Out[46]: [4, 7]

In [47]: d["l"]
Out[47]: [2, 3, 9]

If you just wanted the index for a particular letter you could use a list comp again using enumerate:

inds = [ind for ind, ch in enumerate(s) if ch == "o" ]

For you while logic you need to go from index + 1:

 string.find('o', index + 1)

If you don't you will simply keep finding the same letter at the same index and loop infinitely.

If you want to replace letters, create a mapping with a dict and use dict.get to do the replacing:

d = {"A": "E", "B": "X", "C": "M"}
s = "BACK"
print("".join([d.get(ch, ch) for ch in s]))

Answer 2

I agree with everything @Padraic Cunningham said (+1). To change the letters of certain letters, you could make a function that makes use of the replace method.

def modify(string):
    string = string.lower()  # changes all letters to lowercase
    string = string.replace("a","e")  # changes 'a' to 'e'
    string = string.replace("b","x")  # changes 'b' to 'x'
    string = string.replace("c","m")  # changes 'c' to 'm'
    return string


>>> text = "Beyonce is awesome!"
>>> print text
Beyonce is awesome!

>>> text = modify(text)
>>> print text
xeyonme is ewesome!