.. py:currentmodule:: tulip
Creating and manipulating graphs
================================
Creating a new graph
--------------------
To create a new Tulip graph from Python, the :func:`tlp.newGraph()` function has to be used.
It returns an empty graph which is an instance of the :class:`tlp.Graph` class. ::
graph = tlp.newGraph()
Importing / exporting a graph using the TLP file format
--------------------------------------------------------
TLP is the Tulip format to save a graph and its associated data to a file. The extension of
the file can be .tlp or .tlp.gz (compressed version).
Loading a graph from a TLP file
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
To load a graph saved in TLP into a Python oject, the :func:`tlp.loadGraph` function has to be used. It loads
the graph described in the file and its associated data and returns an instance of the :class:`tlp.Graph`.
For instance, the sample code below imports the graph saved to the file /home/foo/savedgraph.tlp::
graph = tlp.loadGraph("/home/foo/savedgraph.tlp")
Saving a graph to a TLP file
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
To save an instance of a :class:`tlp.Graph` class to a TLP file, the :func:`tlp.saveGraph` function has to be used. It saves
the graph and its associated data into a file.
For instance, the sample code below exports a graph to the file /home/foo/mygraph.tlp::
tlp.saveGraph(graph, "/home/foo/mygraph.tlp")
Adding / Removing elements in the graph
----------------------------------------
The graph structure can be freely modified through dedicated methods of the :class:`tlp.Graph` class (see :ref:`Modification of the graph structure `) . Below is a list of some of these methods :
* Adding elements to the graph : :meth:`tlp.Graph.addNode`, :meth:`tlp.Graph.addEdge`
* Removing elements from the graph : :meth:`tlp.Graph.delNode`, :meth:`tlp.Graph.delEdge`, :meth:`tlp.Graph.clear`
Iterating over graph elements
------------------------------
The :class:`tlp.Graph` class provides several iterators on the graph structure (see :ref:`Iterators on the graph structure `).
The sample code below illustrates the syntax to perform an iteration over all the nodes of a graph.::
for n in graph.getNodes():
degree = graph.deg(n)
print("the degree of", n, "is", degree)