feat: added write_graph_graphml()

Author: ntamas

docs/fragments/igraph_write_graph_edgelist.txt

@@ -0,0 +1,14 @@
+Writes the graph in plain edge list format to an output stream.
+
+THe plain edge list format records the structure of the graph _only_ and the
+vertices of the graph will be referred to as numeric vertex IDs instead of
+vertex names.
+
+See `write_graph_ncol()` if you have vertex names and you want to use them
+in the output file instead of IDs.
+
+Parameters:
+    graph: the graph to write
+    outstream: the output file or stream to write the graph to. May be a
+        filename, a path-like object or a file-like object if it is backed
+        by a low-level file handle

docs/fragments/igraph_write_graph_graphml.txt

@@ -0,0 +1,12 @@
+Writes the graph in GraphML format to an output stream.
+
+The GraphML format preserves numeric, string and boolean attributes.
+
+Parameters:
+    graph: the graph to write
+    outstream: the output file or stream to write the graph to. May be a
+        filename, a path-like object or a file-like object if it is backed
+        by a low-level file handle
+    prefixattr: whether to put a prefix in front of the attribute names to
+        ensure uniqueness if the graph has vertex and edge (or graph)
+        attributes with the same name

poetry.lock

@@ -16,6 +16,7 @@ pytest-cov = "^4.0.0"
 richbench = "^1.0.3"
 igraph = "^0.10.6"
 stimulus = { git = "https://github.com/igraph/stimulus.git", tag = "0.15.0" }
+pytest-datadir = "^1.4.1"
 
 [tool.poetry.group.doc.dependencies]
 mkdocs-material = "^9.1.21"
@@ -59,6 +60,7 @@ python =
 deps =
     pytest
     pytest-cov
+    pytest-datadir
 commands = pytest tests
 
 [testenv:type]

pyproject.toml

@@ -5083,7 +5083,21 @@ def read_graph_dl(instream: FileLike, directed: bool = True) -> Graph:
 
 
 def write_graph_edgelist(graph: Graph, outstream: FileLike) -> None:
-    """Type-annotated wrapper for ``igraph_write_graph_edgelist``."""
+    """Writes the graph in plain edge list format to an output stream.
+
+    THe plain edge list format records the structure of the graph _only_ and the
+    vertices of the graph will be referred to as numeric vertex IDs instead of
+    vertex names.
+
+    See `write_graph_ncol()` if you have vertex names and you want to use them
+    in the output file instead of IDs.
+
+    Parameters:
+        graph: the graph to write
+        outstream: the output file or stream to write the graph to. May be a
+            filename, a path-like object or a file-like object if it is backed
+            by a low-level file handle
+    """
     # Create exit stack for graceful cleanup
     with ExitStack() as py__stack:
 
@@ -5142,7 +5156,19 @@ def write_graph_leda(graph: Graph, outstream: FileLike, names: str = "name", wei
 
 
 def write_graph_graphml(graph: Graph, outstream: FileLike, prefixattr: bool = True) -> None:
-    """Type-annotated wrapper for ``igraph_write_graph_graphml``."""
+    """Writes the graph in GraphML format to an output stream.
+
+    The GraphML format preserves numeric, string and boolean attributes.
+
+    Parameters:
+        graph: the graph to write
+        outstream: the output file or stream to write the graph to. May be a
+            filename, a path-like object or a file-like object if it is backed
+            by a low-level file handle
+        prefixattr: whether to put a prefix in front of the attribute names to
+            ensure uniqueness if the graph has vertex and edge (or graph)
+            attributes with the same name
+    """
     # Create exit stack for graceful cleanup
     with ExitStack() as py__stack:
 

src/igraph_ctypes/_internal/functions.py

@@ -1,3 +1,3 @@
-from ._internal.functions import write_graph_edgelist
+from ._internal.functions import write_graph_edgelist, write_graph_graphml
 
-__all__ = ("write_graph_edgelist",)
+__all__ = ("write_graph_edgelist", "write_graph_graphml")

src/igraph_ctypes/io.py

@@ -2,7 +2,7 @@
 from pytest import fixture, raises
 
 from igraph_ctypes.constructors import create_graph_from_edge_list
-from igraph_ctypes.io import write_graph_edgelist
+from igraph_ctypes.io import write_graph_edgelist, write_graph_graphml
 
 
 @fixture
@@ -11,9 +11,9 @@ def simple_graph():
     return g
 
 
-def test_write_graph_edgelist(simple_graph, tmp_path):
+def test_write_graph_edgelist(simple_graph, tmp_path, datadir):
     path: Path = tmp_path / "edges.txt"
-    expected = "0 1\n1 2\n1 3\n2 3\n"
+    expected = (datadir / "simple_graph.txt").read_text()
     path_str = str(path)
 
     # Write to a file specified by its filename
@@ -48,3 +48,14 @@ def test_write_graph_edgelist(simple_graph, tmp_path):
     with raises(OSError):
         with path.open("r") as fp:
             write_graph_edgelist(simple_graph, fp)
+
+
+def test_write_graph_graphml(simple_graph, tmp_path, datadir):
+    path: Path = tmp_path / "edges.graphml"
+    expected = (datadir / "simple_graph.graphml").read_text()
+    path_str = str(path)
+
+    # Write to a file specified by its filename
+    write_graph_graphml(simple_graph, path_str)
+    assert path.read_text() == expected
+    path.unlink()

tests/test_write_graph.py

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<graphml xmlns="http://graphml.graphdrawing.org/xmlns"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://graphml.graphdrawing.org/xmlns
+         http://graphml.graphdrawing.org/xmlns/1.0/graphml.xsd">
+<!-- Created by igraph -->
+  <graph id="G" edgedefault="undirected">
+    <node id="n0">
+    </node>
+    <node id="n1">
+    </node>
+    <node id="n2">
+    </node>
+    <node id="n3">
+    </node>
+    <edge source="n0" target="n1">
+    </edge>
+    <edge source="n1" target="n2">
+    </edge>
+    <edge source="n2" target="n3">
+    </edge>
+    <edge source="n1" target="n3">
+    </edge>
+  </graph>
+</graphml>

tests/test_write_graph/simple_graph.graphml

@@ -0,0 +1,4 @@
+0 1
+1 2
+1 3
+2 3