In #136061,
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# Ick. It may require *inserting* spaces if we back up over a |
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# tab character! This is written to be clear, not fast. |
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tabwidth = self.tabwidth |
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have = len(chars.expandtabs(tabwidth)) |
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assert have > 0 |
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want = ((have - 1) // self.indentwidth) * self.indentwidth |
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# Debug prompt is multilined.... |
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ncharsdeleted = 0 |
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while True: |
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chars = chars[:-1] |
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ncharsdeleted = ncharsdeleted + 1 |
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have = len(chars.expandtabs(tabwidth)) |
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if have <= want or chars[-1] not in " \t": |
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break |
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text.undo_block_start() |
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text.delete("insert-%dc" % ncharsdeleted, "insert") |
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if have < want: |
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text.insert("insert", ' ' * (want - have), |
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self.user_input_insert_tags) |
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text.undo_block_stop() |
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return "break" |
is mentioned as an area of code with quadratic complexity, which may lead to performance issues; though this is unlikely to be of large impact in practice because attackers with the ability to get a huge file loaded and/or modify configuration files to change the tab width can do much worse things than getting IDLE to hang on hitting backspace.
However, the complexity there comes from a loop which handles situations (files with tabs) that either cannot or should not occur; in the current default IDLE, you can't put tabs, and a space after a tab should just be deleted in a file coming from elsewhere as in indicated in #134874 (comment). Therefore, simplifying the function specification and/or deprecating IDLE to handle tabs (which we should do) will allow elimination of this piece of obsolete code, as indicated in #136061 (comment).
