Normally, you would just do:
s = s[:-3] + s[-2:]
The s[:-3] gives you a string up to, but not including, the comma you want removed ("this is a string") and the s[-2:] gives you another string starting one character beyond that comma (" a").
Then, joining the two strings together gives you what you were after ("this is a string a").
python - Ways to slice a string? - Stack Overflow
What is the difference between String.slice and String.substring?
Return slice of struct of string?
How to keep both a String and it's slice in a struct?
This is a self-referential struct, and it isn't very well supported by rust. Your From implementation only works because you're making a copy of the &'a str you're passing in, but that doesn't seem to be what you want by the title.
What are you trying to do? Maybe you can get the indices from split and save those as an alternative.
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Normally, you would just do:
s = s[:-3] + s[-2:]
The s[:-3] gives you a string up to, but not including, the comma you want removed ("this is a string") and the s[-2:] gives you another string starting one character beyond that comma (" a").
Then, joining the two strings together gives you what you were after ("this is a string a").
A couple of variants, using the "delete the last comma" rather than "delete third last character" are:
s[::-1].replace(",","",1)[::-1]
or
''.join(s.rsplit(",", 1))
But these are pretty ugly. Slightly better is:
a, _, b = s.rpartition(",")
s = a + b
This may be the best approach if you don't know the comma's position (except for last comma in string) and effectively need a "replace from right". However Anurag's answer is more pythonic for the "delete third last character".
slice() works like substring() with a few different behaviors.
Syntax: string.slice(start, stop);
Syntax: string.substring(start, stop);
What they have in common:
- If
startequalsstop: returns an empty string - If
stopis omitted: extracts characters to the end of the string - If either argument is greater than the string's length, the string's length will be used instead.
Distinctions of substring():
- If
start > stop, thensubstringwill swap those 2 arguments. - If either argument is negative or is
NaN, it is treated as if it were0.
Distinctions of slice():
- If
start > stop,slice()will return the empty string. ("") - If
startis negative: sets char from the end of string, exactly likesubstr(). - If
stopis negative: sets stop to:string.length – Math.abs(stop)(original value), except bounded at 0 (thus,Math.max(0, string.length + stop)) as covered in the ECMA specification.
Source: Rudimentary Art of Programming & Development: Javascript: substr() v.s. substring()
TL;DR:
- If you know the index (the position) on which you'll stop (but NOT include), use
slice(). - If you know the length of characters to be extracted, you could use
substr(), but that is discouraged as it is deprecated.
Otherwise, read on for a full comparison
Syntax
string.slice(start,end)string.substr(start,length)string.substring(start,end)
Note #1: slice()==substring()
What it does?
slice()extracts parts of a string and returns the extracted parts in a new string.substr()extracts parts of a string, beginning at the character at the specified position, and returns the specified number of characters.substring()extracts parts of a string and returns the extracted parts in a new string.
Note #2: slice()==substring()
Changes the Original String?
slice()doesn'tsubstr()doesn'tsubstring()doesn't
Note #3: slice()==substr()==substring()
Using Negative Numbers as an Argument
slice()selects characters starting from the end of the stringsubstr()selects characters starting from the end of the stringsubstring()doesn't perform
Note #4: slice()==substr()
If the First Argument is Greater than the Second
slice()doesn't performsubstr()since the Second Argument is NOT a position, but length value, it will perform as usual, with no problemssubstring()will swap the two arguments, and perform as usual
The First Argument
slice()required; starting Indexsubstr()required; starting Indexsubstring()required; starting Index
Note #5: slice()==substr()==substring()
The Second Argument
slice()optional; the position (up to, but not including) where to end the extractionsubstr()optional; the number of characters to extractsubstring()optional; the position (up to, but not including) where to end the extraction
Note #6: slice()==substring()
What if the Second Argument is Omitted?
slice()selects all characters from the start-position to the end of the stringsubstr()selects all characters from the start-position to the end of the stringsubstring()selects all characters from the start-position to the end of the string
Note #7: slice()==substr()==substring()
So, you can say that there's a difference between slice() and substr(), while substring() is basically a copy of slice().
If you want substr's functionality:
"foobarbaz".substr(index, length);
without using a deprecated feature, you can just do:
"foobarbaz".substring(index, length + index);
And get the exact same results bar all of the edge-cases, like negative index/length.