[issue39823] Disassembly - improve documentation for bytecode instruction class and set source line no. attribute for every instruction

[Irit Katriel]

Irit Katriel  added the comment:

I don't think this change should be made - it would generate the same 
information in a slightly different format, which will break existing code 
while not making it possible to do anything we can't do now.

--
nosy: +iritkatriel
versions: +Python 3.11 -Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue39823] Disassembly - improve documentation for bytecode instruction class and set source line no. attribute for every instruction

[S Murthy]

S Murthy  added the comment:

Docstring for `Instruction` should be more precise. ATM the description of 
`starts_line` is

line started by this opcode (if any), otherwise None

I think "source line started ..." would be a bit more precise and accurate.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue39823] Disassembly - improve documentation for bytecode instruction class and set source line no. attribute for every instruction

[S Murthy]

New submission from S Murthy :

I note that on disassembling a piece of source code (via source strings or code 
objects) the corresponding sequence of bytecode instruction objects 
(https://docs.python.org/3/library/dis.html#dis.Instruction) do not always have 
the `starts_line` attribute set - the storage and display of this line no. 
seems to be based on whether a given instruction is the first in a block of 
instructions which implement a given source line.

I think it would be better, for mapping source and logical lines of code to 
bytecode instruction blocks, to set `starts_line` for every instruction, and 
amend the bytecode printing method (`dis._disassemble_bytes`) to keep the 
existing behaviour by detecting whether an instruction is the first line of an 
instruction block.

ATM `Instruction` objects are created and generated within this loop in 
`dis._get_bytecode_instructions`:

def _get_instructions_bytes(code, varnames=None, names=None, constants=None,
  cells=None, linestarts=None, line_offset=0):
"""Iterate over the instructions in a bytecode string.

Generates a sequence of Instruction namedtuples giving the details of each
opcode.  Additional information about the code's runtime environment
(e.g. variable names, constants) can be specified using optional
arguments.

"""
labels = findlabels(code)
starts_line = None
for offset, op, arg in _unpack_opargs(code):
if linestarts is not None:
starts_line = linestarts.get(offset, None)
 ...
 ...

So it's this line

starts_line = linestarts.get(offset, None)

which currently causes `starts_line` to be to set to `None` for every 
instruction which isn't the first in an instruction block - linestarts is a 
dict of source line numbers and offsets of the first instructions starting the 
corresponding instruction blocks.

My idea is to (1) change that line above to
 
starts_line = linestarts.get(offset, starts_line)

which ensures every instruction will have the corresponding source line no. 
set, (2) amend `Instruction._disassemble` to add a new optional argument 
`print_start_line` with default of `True` to determine whether to print the 
source line no., and (3) amend `dis._disassemble_bytes` to accept a new 
optional argument `start_line_by_block` with a default of `True` which can be 
used to preserve existing behaviour of printing source line numbers by 
instruction block.

I was wondering whether this sounds OK, if so, I am happy to submit a PR.

--
components: Library (Lib)
messages: 363140
nosy: smurthy
priority: normal
severity: normal
status: open
title: Disassembly - improve documentation for bytecode instruction class and 
set source line no. attribute for every instruction
type: enhancement
versions: Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com