Debugging your Lager Python program
===================================

When using ``lager python``, a `remote pdb <https://docs.python.org/3/library/pdb.html>`_ tunnel is automatically established. To use it, add a call to `breakpoint() <https://docs.python.org/3/library/functions.html#breakpoint>`_ in your code, and then use telnet to connect to port ``5555`` on host ``127.0.0.1``.

Simple pdb example
---------------------
.. code-block:: python
   :emphasize-lines: 9
   :caption: breakpoint.py
   :name: Simple breakpoint example

   def foo():
      print("hello")

   def bar():
      print("world")

   def main():
      print("started...")
      breakpoint()
      foo()
      bar()

   if __name__ == '__main__':
      main()


Save the above listing as ``breakpoint.py``

.. code-block:: console

    ➜  lager python breakpoint.py
    started...
    RemotePdb session open at 0.0.0.0:5555, waiting for connection ...
    RemotePdb session open at 0.0.0.0:5555, waiting for connection ...


Then in a separate terminal window:

.. code-block:: console

    ➜  telnet 127.0.0.1 5555
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    > /tmp/tmpw5kcntdp.py(10)main()
    -> foo()