I noticed since the new parser implementation, the debug mode in the tokeniser is no longer working.

This is the case for 3.9.0 and also 3.9.1rc1. Running python3.9 with a simple application like this:

 # Demo application
 def my_function():
   proceed

Does not output anything

> python3.9 -d ~/PycharmProjects/cpython-book-samples/13/test_tokens.py

> 
Produces no output

Whereas python3.10 (the latest alpha) outputs the expected results

Hi Anthony,

could it be that your 3.9 is not a debug build, while the others are? We only enable parser debug ouput when Python has been build --with-pydebug.

Building the 3.9.0 tag --with-pydebug works fine for me.

I cannot reproduce it either in 3.9. Building 3.9 in debug mode and using -d works as expected

Also, note the -d flag activates the debug mode **in the parser**, not in the tokenizer.

thanks, it would be great if this were documented in the --help section like the other options which require a debug build (-X showrefcount)

In PyConfig, I chose to name the option "parser_debug" rather than the very generic "debug" name :-)

"""
Parser debug mode. If greater than 0, turn on parser debugging output (for expert only, depending on compilation options).

Incremented by the -d command line option. Set to the PYTHONDEBUG environment variable value.
"""

https://docs.python.org/dev/c-api/init_config.html#c.PyConfig.parser_debug

> thanks, it would be great if this were documented in the --help section like the other options which require a debug build (-X showrefcount)

PyConfig.show_ref_count documentation explains that a debug build is required:

"Need a debug build of Python (Py_REF_DEBUG macro must be defined)."

https://docs.python.org/dev/c-api/init_config.html#c.PyConfig.show_ref_count

By the way, it would be nice to add a link on "debug build" to explain how to detect if Python is built in debug mode and how to build Python in debug mode.

New changeset 99b594404d364b363c184f48338d6ee81bee26dd by Pablo Galindo in branch 'master':
bpo-42521: Add note about 'Python -d' only working on debug builds (GH-23607)
https://github.com/python/cpython/commit/99b594404d364b363c184f48338d6ee81bee26dd

New changeset 9b34f34aa929941576a69a6f7de77f1fb0b96ed6 by Miss Islington (bot) in branch '3.9':
bpo-42521: Add note about 'Python -d' only working on debug builds (GH-23607)
https://github.com/python/cpython/commit/9b34f34aa929941576a69a6f7de77f1fb0b96ed6