Replacing a character from a certain index [duplicate]
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.
Something like this maybe?
middle = ? # (I don't know how to get the middle of a string)
if str[middle] != char:
str[middle].replace('')
Solution 1:
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'
Solution 2:
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'
Solution 3:
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'
.
Solution 4:
# 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