How to print a substring between two patterns if an offset is provided as an input-CodePudding

How can we print a substring that occurs between two patterns? We are also provided an offset of a character in the string as an input to choose which substring needs to be printed.

E.g.

string = '<p >A quick brown fox</p><p >Jumps over</p>'

The substring that needs to be printed is between the patterns "> and </p>.

If the offset provided is 20 then A quick brown fox should be printed. If the offset provided is 55 then Jumps over should be printed, this offset should be received as an input.

CodePudding user response：

The offset seems to be taken as a starting point for searching the nearest "> to the left and </p> to the right.

<p >A quick brown fox</p><p >Jumps over</p>
                    ^                                  ^
                 offset 20                          offset 55

In other words, find the rightmost "> in the substring from the beginning to the offset, and the leftmost </p> in the substring from the offset to the end.

For this, there are the find and rfind string methods.

>>> string.rfind('">', 0, 20)
13
>>> string.rfind('">', 0, 55)
49
>>> string.find('</p>', 20)
32
>>> string.find('</p>', 55)
61

Now you can use these indices to slice the string. You have to account for the fact that rfind returns the index before ">, but you need to slice after it, so you have to add its length (2) to the start index of the slice.

>>> start = string.rfind('">', 0, 20)   2
>>> end = string.find('</p>', 0, 20)
>>> string[start:end]
'A quick brown fox'