[issue39537] Change line number table format

[Serhiy Storchaka]

Serhiy Storchaka <storchaka+cpython at gmail.com> added the comment:

I planned to add a table for end line numbers, so every instruction will be associated with a range of lines.

For example, in

  x = {
    a,
    b
  }

the BUILD_SET instruction will be associated with lines 1-4. Currently it is associated only with line 1, and was associated with line 3 in 3.7.

In

  x = (
    a
    +
    b
  )

the BINARY_ADD instruction will be associated with lines 2-4. Currently it is associated with line 2, and was associated with line 4 in 3.7. The proposition about associating it with line 3 (containing the "+" operator) was rejected before.

In

  x = (
    a
    .
    b
  )

the LOAD_ATTR instruction will be associated with lines 2-4. Currently it is associated with line 2. The AST does not contain information about lines of "." and "b" tokens, but it contains information about the start and the end positions of "a.b".

This will help tools like coverage.py which are confused be executing the same line several times and may allow to generate more informative tracebacks.

As for END_ASYNC_FOR, it will be associated with the range of the "async for" statement.

Maybe we could use more efficient format for encoding start and end line numbers.

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nosy: +serhiy.storchaka

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<https://bugs.python.org/issue39537>
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