[Python-ideas] Interactive trace function

Gerald Britton gerald.britton at gmail.com
Fri Mar 20 14:54:09 CET 2009

Years ago I worked for a while in REXX.  It was a fairly advanced
scripting language for its time and we used it on some substantial
mainframe projects.  One thing that I liked and miss in Python is the
"trace" statement.

Basically, you could insert a "trace" statement in a REXX program and
then, when you ran it, it would step through the program a line at a
time.  This gave you the chance to follow your code through tricky
sections and display variables after each step.  I know it saved me
hours of troubleshooting of tricky problems.

I would like to know if anyone has ever proposed something similar for
Python.  It would work something like this:

1. In an interactive session, you could issue a trace command.
Thereafter, whatever you ran would be done a step at a time, with a
terminal prompt after every statement for you to print anything you
like that would help you understand the state of the program at that

2. From the command line, you could add a --trace option, or something
like it, to ask Python to launch the program interactively with trace
enabled, which would work as described above.

3. If you have a problematic piece of code, you could insert a trace
statement just before the troubled section. Then when you ran the
program, when it came to the trace statement, it would begin an
interactive trace at that point as described above. (You would have to
start your program from the command line for this to make sense.)

Has something like this ever come up before?  Is there a way to do this today?

Gerald Britton

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