[Python] #line in python

No [easy] way to go from bytecodes back to AST, but I see no reason why you
can't create a new code object with your filename and line numbers and then
create a new function using your modified code object.

If you don't have a 1:1 correspondence of lines then you'll need to pick
out all the existing line numbers from the code object co_lnotab and modify
them: see dis.py findlinestarts() for how to do this.

Classes would be harder: the decorator doesn't run until after the class
body has executed, so you can't change the line numbers that way until it's
too late. The only thing I can think would be to put all of the generated
code inside a function and fix up that function with a decorator that scans
the bytecode to find all contained classes and fix them up.

Or you could generate a .pyc file and then fix up line numbers in the whole
file: see
http://nedbatchelder.com/blog/200804/the_structure_of_pyc_files.html for
some code that shows you what's in a .pyc

Duncan Booth wrote
________________________________________________________________________
My latest concept is to produce code that rewrites itself. Suppose the
naive file would be
----------- mycode.py (naive) --------------------------------
class SomeClass:
"class comment"

def some_function(self, bar):
pass
--------- end -------------------------------

Protect that code by putting an "if 0:" in front of it and indenting
each line one space. Than prepend a bit of code to do the rewriting,
and add indicators of the original line numbers.

----------- mycode.py (after wrapping) -------------
from detangle import detangle
detangle("mycode.py", "mycode.nw")
if 0:
# original code goes here
class SomeClass:
"class comment"
#and when line numbering changes
#line 35
def some_function(self, bar):
pass
------------- end -------------------
I would write detangle so that it scans through the file in which it
appears (named in the first argument), rewriting so that it appears to
come from the original file (mycode.nw) given in the second argument.

The scanning would look for the "if 0:" in the file. At that point it
would accumulate code by reading lines and stripping the leading space.
If it found a #line directive it would remember it and then remove it
from the string it was accumulating. Finally, detangle would would
pass the string of code to ast.compile, catching any syntax errors and
rewriting the file and line number (I might rewrite columns too with an
extension) and then rethrowing them.

If compilation succeeded detangle could rewrite the AST and then exec
it.

Ross

This (written for Python 3.x, needs some attribute names changing for
Python 2.x:

import functools
def source_line(lineno, filename = None):
def decorator(f):
c = f.__code__
code = type(c)(
c.co_argcount, c.co_kwonlyargcount, c.co_nlocals,
c.co_stacksize, c.co_flags, c.co_code,
c.co_consts, c.co_names, c.co_varnames,
c.co_filename if filename is None else filename,
c.co_name,
lineno,
c.co_lnotab, c.co_freevars, c.co_cellvars)
f.__code__ = code
return f
return decorator


@source_line(43, 'foo.bar')
def foo():
"""This is foo"""
for i in range(10):
bar()

@source_line(665, 'evil.txt')
def bar():
raise RuntimeError("oops")

if __name__=='__main__':
import traceback
try:
foo()
except RuntimeError as ex:
traceback.print_exc()

When you run it the output looks something like this (if you create a
file evil.txt with 667 lines):

Traceback (most recent call last):
File "C:\temp\foo.py", line 30, in <module>
foo()
File "foo.bar", line 47, in foo
File "evil.txt", line 667, in bar
Evil line 667
RuntimeError: oops