[Python-Dev] co_firstlineno on decorated functions (original) (raw)

Terry Reedy tjreedy at udel.edu
Tue Aug 3 19:25:28 CEST 2010

On 8/3/2010 8:48 AM, Antoine Pitrou wrote:

On Tue, 3 Aug 2010 22:25:01 +1000 Nick Coghlan<ncoghlan at gmail.com> wrote:

On Tue, Aug 3, 2010 at 1:40 PM, Eli Bendersky<eliben at gmail.com> wrote:

The first print out correctly specifies the line "def foo" is in. However, the second one points to the line with "@dummydecorator" instead of "def bar". [Python 2.6]

The side-effects of this behavior can be easily seen in the output of modules like trace and profile. Would you say it's normal, or could this be considered a bug? Since the decorator is as much a part of the function definition as the def line is, I would say that it is correct (the name says "firstlineno", not "deflineno"). That's debatable. Since writing: @b def a(): ... is equivalent to: def a(): ... a = b(a)

The difference is that 'a=b(a)' is a standalone statement which could moved down with other statements interposed, while '@b' is neither a statement nor expression but a def statement prefix, and is documented as such.

A dynamic difference between the constructs, as least with CPython, is that the decorator form does just one namespace binding instead of two.

and in the latter case cofirstlineno points to the "def a()" line.

Furthermore, cofirstlineno is an attribute of the code object, not the function object, so it shouldn't ideally depend on whether a decorator was applied or not.

Perhaps. A practical consideration is that it is easier to search forward from the first '@' line to the 'def' line than the reverse.

-- Terry Jan Reedy

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