Interactively tracing execution of a command

sage.misc.trace.trace(code, preparse=True)[source]

Evaluate Sage code using the interactive tracer and return the result. The string code must be a valid expression enclosed in quotes (no assignments - the result of the expression is returned). In the Sage notebook this just raises a NotImplementedException.

INPUT:

  • code – string

  • preparse – boolean (default: True); if True, run expression through the Sage preparser

REMARKS: This function is extremely powerful! For example, if you want to step through each line of execution of, e.g., factor(100), type

sage: from sage.misc.trace import trace
sage: trace("factor(100)")             # not tested

>>> from sage.all import *
>>> from sage.misc.trace import trace
>>> trace("factor(100)")             # not tested

from sage.misc.trace import trace
trace("factor(100)")             # not tested

then at the (Pdb) prompt type s (or step), then press Return over and over to step through every line of Python that is called in the course of the above computation. Type ? at any time for help on how to use the debugger (e.g., l lists 11 lines around the current line; bt gives a back trace, etc.).

Setting a break point: If you have some code in a file and would like to drop into the debugger at a given point, put the following code at that point in the file:

import pdb; pdb.set_trace()

For an article on how to use the Python debugger, see http://www.onlamp.com/pub/a/python/2005/09/01/debugger.html