[New-bugs-announce] [issue42373] PEP 626 does not specify behavior of tracing for keywords.

[Mark Shannon]

New submission from Mark Shannon <mark at hotpy.org>:

PEP 626 doesn't cover which keywords are to be traced if they occur on a line by themselves.

Some keywords, like `break`, in Python have behavior associated with them.
Others, like `else` are just syntax and don't do anything.
Currently, it is not clear which keywords get traced and which do not.


I'd like to update the PEP to include the following:

Keywords can be broken down into five groups.
1. Must have an attendant expression ( "if", "while", "for", "await")
   These keywords are not traced, since their expressions are.
2. Have an optional expression and perform non-local control flow ( "return", "yield", "raise", "except" )
   These keywords are traced. If on a different line from the expression, they will generate additional events.
3. Pure syntax ( "else", "try", "finally" )
   These keywords are not traced.
4. Local control flow ( "break", continue", "pass" )
   These keywords are traced
5. Expressions ( "None", "True", "False" )
   Treated like other expressions


Examples:

1. if (
2.    test
3. ):

will generate an event for line 2.


1. return (
2.    x
3. ):

will generate an event for line 2, then line 1.

1. try:
2.    None
3. finally:
4.    pass

Will generate an event for line 2, then line 4.


Note that whatever changes, the invariant remains that if a line is in `co_lines()` then it will generate trace events, and if it isn't then it won't.

----------
assignee: Mark.Shannon
messages: 381114
nosy: Mark.Shannon, nedbat, pablogsal
priority: normal
severity: normal
status: open
title: PEP 626 does not specify behavior of tracing for keywords.
versions: Python 3.10

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42373>
_______________________________________