Python 替换某个索引中的字符
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Replacing a character from a certain index
提问by Jordan Baron
How can I replace a character in a string from a certain index? For example, I want to get the middle character from a string, like abc, and if the character is not equal to the character the user specifies, then I want to replace it.
如何从某个索引替换字符串中的字符？例如，我想从字符串中获取中间字符，例如abc，如果该字符不等于用户指定的字符，那么我想替换它。
Something like this maybe?
也许像这样的东西？
middle = ? # (I don't know how to get the middle of a string)
if str[middle] != char:
str[middle].replace('')
回答by ti7
As strings are immutablein Python, just create a new string which includes the value at the desired index.
由于字符串在 Python 中是不可变的，只需创建一个新字符串，其中包含所需索引处的值。
Assuming you have a string s, perhaps s = "mystring"
假设你有一个字符串s，也许s = "mystring"
You can quickly (and obviously) replace a portion at a desired index by placing it between "slices" of the original.
您可以通过将其放置在原始“切片”之间来快速（并且显然）替换所需索引处的部分。
s = s[:index] + newstring + s[index + 1:]
You can find the middle by dividing your string length by 2 len(s)/2
您可以通过将字符串长度除以 2 来找到中间值 len(s)/2
If you're getting mystery inputs, you should take care to handle indices outside the expected range
如果您收到神秘输入，则应注意处理超出预期范围的索引
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
这将作为
replacer("mystring", "12", 4)
'myst12ing'
回答by Willem Van Onsem
Strings in Python are immutablemeaning you cannot replaceparts of them.
Python 中的字符串是不可变的，这意味着您无法替换它们的一部分。
You can however create a new stringthat is modified. Mind that this is not semantically equivalentsince other references to the old string will not be updated.
但是，您可以创建一个经过修改的新字符串。请注意，这在语义上并不等效，因为不会更新对旧字符串的其他引用。
You could for instance write a function:
例如，您可以编写一个函数：
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:
然后例如调用它：
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.
如果不提供替换，新字符串将不包含要删除的字符，您可以提供任意长度的字符串。
For instance:
例如：
replace_str_index('hello?bye',5)
will return 'hellobye'; and:
会回来'hellobye'；和：
replace_str_index('hello?bye',5,'good')
will return 'hellogoodbye'.
会回来'hellogoodbye'。
回答by Jacob Malachowski
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.
您不能替换字符串中的字母。将字符串转换为列表，替换字母，然后将其转换回字符串。
>>> s = list("Hello world")
>>> s
['H', 'e', 'l', 'l', 'o', ' ', 'z', 'o', 'r', 'l', 'd']
>>> s[int(len(s) / 2)] = '-'
>>> s
['H', 'e', 'l', 'l', 'o', '-', 'W', 'o', 'r', 'l', 'd']
>>> "".join(s)
'Hello-World'
回答by Shivam Bharadwaj
# 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
I/P : 猫坐在垫子上
O/P : The cat slept on the mat
O/P : 猫睡在垫子上
