debugging.txt

Saturday January 23, 2016
README
Waheed Brown

CONTENTS
--------
1. Python Debugger
2. Valgrind
3. Bytecode - .pyc Files

1. PYTHON DEBUGGER

Python Debugger (Python 2.x):
https://docs.python.org/2/library/pdb.html

- The below trace() method is by far the easiest for debugging, without
  command line arguments.
- If you want to provide command line arguments to the program then use
  the below "$ python -d" method.


METHOD 1:

Set breakpoint:
import pdb; pdb.set_trace()

METHOD 2:

$ python -d
>>> import pdb
>>> import test
>>> argv = ['arg1', 'arg2', 'arg3']
>>> pdb.run( 'test.main(argv)' )
...
(Pdb) step
(Pdb) print opt
(Pdb) args # print argument list of current function
(Pd.) print __name__ # print name of current function
(Pdb) continue
...
(Pdb) exit


DEBUGGER COMMANDS:

- [s]tep
- [p]rint

  example:

    > p j, num, i # prints comma separated values in brackets
    > (5, 10, 2)


2. VALGRIND

In order to use Python with Valgrind you need to build the Python source
code [1] with specific options (try to pick the same source code release
number as your default installed Python version):

  $ ./configure --with-pydebug --without-pymalloc --prefix /opt/debugpython/
  $ make OPT=-g
  $ make install

The install location for the binary is:

  /opt/debugpython/bin/python

This means that you need to change the shebang line in any Python code that
you wish to test with Valgrind:

  #!/opt/debugpython/bin/python

Alternatively, you can leave your code unmodified and just point to the
debug Python version when you execute Valgrind:

  $ valgrind /opt/debugpython/bin/python your_program.py

REFERENCES:

1. https://www.python.org/downloads/release
2. https://code.google.com/archive/p/distnumpy/wikis/valgrind.wiki


3. BYTECODE - .pyc FILES

$ python -m your_program.py

This will produce a .pyc file which can be imported as a module
in other Python programs. Mildly obfuscates your code. To
recursively compile all code in nested folders run:

$ python -m compileall