如何将字符偏移量转换为“文本”小部件的列行号位置？

Question

I have a text widget with some text. Within the text from characters 424 to 478 I would like to change its color using tag_add().

The problem is that tag_add() requires positioning in "6.15" format, meaning sixth line fifteenth character. However I don't know how many new lines precede the 424th character nor what is the remainder to calculate the exact column. Is there a method to convert from an absolute byte offset to line/column index?

Answer 1

The text widget supports a limited expression syntax with indexes. Among other things you can add and subtract characters from an index. For example, you can use "1.0 + 100 chars" (or "1.0+100c" ) to mean "line one, character zero, plus 100 characters".

The official python documentation punts on documenting this, choosing to refer you to the offical tcl/tk documentation here: http://tcl.tk/man/tcl8.5/TkCmd/text.htm#M16

This is also documented on the effbot site here: http://effbot.org/tkinterbook/text.htm (see the section "Expressions")

Answer 2

If you are using insert() to add the text, you can specify the tag to use during the insert:

textw.tag_configure('red', background='red')

textw.insert(END, 'Some sample text ', (), 'with a bit of red', 'red', ' in the middle.')

Results in:

Also, depending on how your text is configured you can use:

textw.tag_add('red', 1.424, 1.478)