Added Interface for Netzschleuder .gml.zst files

src/igraph/__init__.py

@@ -213,6 +213,9 @@
     _construct_graph_from_graph_tool,
     _export_graph_to_graph_tool,
 )
+from igraph.io.repositories import(
+    _construct_graph_from_Netzschleuder,
+)
 from igraph.io.random import (
     _construct_random_geometric_graph,
 )
@@ -462,6 +465,9 @@ def __init__(self, *args, **kwds):
     from_graph_tool = classmethod(_construct_graph_from_graph_tool)
     to_graph_tool = _export_graph_to_graph_tool
 
+    # Repositories
+    from_Netzschleuder = classmethod(_construct_graph_from_Netzschleuder)
+
     # Files
     Read_DIMACS = classmethod(_construct_graph_from_dimacs_file)
     write_dimacs = _write_graph_to_dimacs_file

src/igraph/io/repositories.py

@@ -0,0 +1,67 @@
+import os
+import tempfile
+import requests
+import zstandard as zstd
+import igraph as ig
+
+def _construct_graph_from_Netzschleuder(cls=ig.Graph, name: str = None, net: str = None) -> ig.Graph:
+    """
+    Downloads, decompresses, and loads a graph from Netzschleuder into an igraph.Graph.
+
+    Parameters:
+        cls (igraph.Graph, optional): The graph class to use (default: ig.Graph).
+        name (str): The dataset name (e.g., "bison").
+        net (str, optional): The specific network file (defaults to `name`).
+
+    Returns:
+        igraph.Graph: The loaded graph.
+
+    Raises:
+        ValueError: If the dataset or network file does not exist.
+        RuntimeError: If there are issues with download or decompression.
+    """
+    if name is None:
+        raise ValueError("Dataset name must be provided.")
+
+    base_url = "https://networks.skewed.de/net"
+    net = net or name  # Default net name
+
+    # Check dataset existence
+    dataset_url = f"{base_url}/{name}"
+    if requests.head(dataset_url, timeout=5).status_code != 200:
+        raise ValueError(f"Dataset '{name}' does not exist at {dataset_url}.")
+
+    # Check network file existence
+    file_url = f"{dataset_url}/files/{net}.gml.zst"
+    if requests.head(file_url, timeout=5).status_code != 200:
+        raise ValueError(f"Network file '{net}.gml.zst' does not exist at {file_url}.")
+
+    try:
+        # Download the compressed file
+        with tempfile.NamedTemporaryFile(delete=False, suffix=".zst") as tmp_zst_file:
+            response = requests.get(file_url, stream=True, timeout=10)
+            response.raise_for_status()
+            tmp_zst_file.write(response.content)
+            tmp_zst_path = tmp_zst_file.name
+
+        # Decompress the file
+        dctx = zstd.ZstdDecompressor()
+        with tempfile.NamedTemporaryFile(delete=False, suffix=".gml") as tmp_gml_file:
+            with open(tmp_zst_path, "rb") as compressed:
+                dctx.copy_stream(compressed, tmp_gml_file)
+            tmp_gml_path = tmp_gml_file.name
+
+        # Load graph using the given class
+        graph = cls.Read_GML(tmp_gml_path)
+
+    except requests.RequestException as e:
+        raise RuntimeError(f"Network error: {e}")
+    except zstd.ZstdError as e:
+        raise RuntimeError(f"Decompression error: {e}")
+    except Exception as e:
+        raise RuntimeError(f"Error processing file: {e}")
+    finally:
+        os.remove(tmp_zst_path)
+        os.remove(tmp_gml_path)
+
+    return graph