Fix: make check in OOT build with absolute path

[babeltrace.git] / doc / python-howto.txt

PYTHON BINDINGS
----------------

This is a brief howto for using the Babeltrace Python module.


INSTALLATION:

By default, the Python bindings are not generated.
If you wish to generate and install the Python bindings, you can use the
--enable-python-bindings configure option.

  $ ./configure --enable-python-bindings

The Python module is automatically generated using SWIG, therefore the
swig2.0 package on Debian/Ubuntu is requied.


USAGE:

Once installed, the Python module can be used by importing it in Python.
In the Python interpreter:

  >>> import babeltrace

Then the starting point is to create a context and add a trace to it.

  >>> ctx = babeltrace.Context()
  >>> ctx.add_trace("path/to/trace", <format>)

Where <format> is a string containing the format name in which the trace
was produced.  To print a list of available formats to the standard
output, it is possible to use the print_format_list function.

  >>> out = babeltrace.File(None)	# This returns stdout
  >>> babeltrace.print_format_list(out)

When a trace is added to a context, it is opened and ready to read using
an iterator.  While creating an iterator, optional starting and ending
position may be specified.  So far, only ctf iterator are supported.

  >>> begin_pos = babeltrace.IterPos(babeltrace.SEEK_BEGIN)
  >>> iterator = babeltrace.ctf.Iterator(ctx, begin_pos)

From there, it is possible to read the events.

  >>> event = iterator.read_event()

It is simple to obtain the timestamp of that event.

  >>> timestamp = event.get_timestamp()

Let's say that we want to extract the prev_comm context info for a
sched_switch event.  To do so, it is needed to set an event scope
with which we can obtain the field wanted.

  >>> if event.get_name == "sched_switch":
  ...   #prev_comm only for sched_switch events
  ...   scope = event.get_top_level_scope(babeltrace.ctf.scope.EVENT_FIELDS)
  ...   field = event.get_field(scope, "_prev_comm")
  ...   prev_comm = field.get_char_array()

It is also possible to move on to the next event.

  >>> ret = iterator.next()		# Move the iterator
  >>> if ret == 0:			# No error occured
  ...   event = iterator.read_event()	# Read the next event

For many usage script examples of the Babeltrace Python module, see the
bindings/python/examples directory.