从某个索引中替换字符

如何替换来自某个索引的字符串中的字符？例如，我想从字符串中获取中间字符，比如 abc，如果字符不等于用户指定的字符，那么我想替换它。

也许是这样的？

middle = ? # (I don't know how to get the middle of a string)


if str[middle] != char:
str[middle].replace('')
364111 次浏览
小开

Strings in Python are immutable meaning you cannot replace parts of them.

You can however create a new string that is modified. Mind that this is not semantically equivalent since other references to the old string will not be updated.

You could for instance write a function:

def replace_str_index(text,index=0,replacement=''):
return '%s%s%s'%(text[:index],replacement,text[index+1:])

And then for instance call it with:

new_string = replace_str_index(old_string,middle)

If you do not feed a replacement, the new string will not contain the character you want to remove, you can feed it a string of arbitrary length.

For instance:

replace_str_index('hello?bye',5)

will return 'hellobye'; and:

replace_str_index('hello?bye',5,'good')

will return 'hellogoodbye'.

小开

You can't replace a letter in a string. Convert the string to a list, replace the letter, and convert it back to a string.

>>> s = list("Hello world")
>>> s
['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd']
>>> s[int(len(s) / 2)] = '-'
>>> s
['H', 'e', 'l', 'l', 'o', '-', 'W', 'o', 'r', 'l', 'd']
>>> "".join(s)
'Hello-World'
小开

As strings are immutable in Python, just create a new string which includes the value at the desired index.

Assuming you have a string s, perhaps s = "mystring"

You can quickly (and obviously) replace a portion at a desired index by placing it between "slices" of the original.

s = s[:index] + newstring + s[index + 1:]

You can find the middle by dividing your string length by 2 len(s)/2

If you're getting mystery inputs, you should take care to handle indices outside the expected range

def replacer(s, newstring, index, nofail=False):
# raise an error if index is outside of the string
if not nofail and index not in range(len(s)):
raise ValueError("index outside given string")


# if not erroring, but the index is still not in the correct range..
if index < 0:  # add it to the beginning
return newstring + s
if index > len(s):  # add it to the end
return s + newstring


# insert the new string between "slices" of the original
return s[:index] + newstring + s[index + 1:]

This will work as

replacer("mystring", "12", 4)
'myst12ing'
小开 
# Use slicing to extract those parts of the original string to be kept
s = s[:position] + replacement + s[position+length_of_replaced:]


# Example: replace 'sat' with 'slept'
text = "The cat sat on the mat"
text = text[:8] + "slept" + text[11:]

I/P : The cat sat on the mat

O/P : The cat slept on the mat

小开

You can also Use below method if you have to replace string between specific index

def Replace_Substring_Between_Index(singleLine,stringToReplace='',startPos,endPos):
    

singleLine = singleLine[:startPos]+stringToReplace+singleLine[endPos:]
    

return singleLine

提交答案