def get_edges():
'''
<Graph>.edges AND <Graph>.edges() return the SAME EdgeView of the edges in the graph
- An EdgeView is a strange data structure
- It require a tuple index to access
- What's really going on? Just look at the library code. It's simple really
- At each tuple index, it stores a Python dict
- This syntax makes more sense than the v1.11 syntax
- Edges are stored as 2-tuples (which are immutable)
-
'''
g = Graph([(1, 5), [5, 5]])
print(type(g.edges)) # <class 'networkx.classes.reportviews.EdgeView'>
print(type(g.edges())) # <class 'networkx.classes.reportviews.EdgeView'>
print(g.edges()) # [(1, 5), (5, 5)]
# Invalid syntax
#print(g.edges[1]) # TypeError: 'int' object is not iterable
# Missing keys
#print(g.edges[0, 1]) # KeyError: 1
#print(g.edges[1, 2]) # KeyError: 2
# Correct syntax
print(type(g.edges[1, 5])) # <class 'dict'>
print(g.edges[1, 5]) # {}
# I can view the 2-tuples but can't modify them
for e in g.edges():
pass
def examine_node_attributes():
'''
A node can contain arbitrary attributes
- The <Graph>.node attribute is a regular Python dict whose key-value pairs are node identifiers and Python dicts
- The documentation says that nodes cannot be added to the graph through <Graph>.node, but the code shows they can!
- However, doing this can mess up the structure of the graph. The newly added node might not have its own Python dict if the update was
done incorrectly
- "Warning: adding a node to G.node does not add it to the graph." Listen to the documentation and never try to add nodes via <Graph>.node
'''
g = Graph([(1, 5), (5, 5)])
print(g.nodes()) # [1, 5]
print(g.edges()) # [(1, 5), (5, 5)]
print(type(g.node)) # <class 'dict'>
# Get the dict of an arbitrary node, but not the node itself (annoying)
print(type(g.node[5])) # <class 'dict'>
print(g.node[5]) # {}
g.node[5]['pet'] = 'cat'
print(g.node[5]) # {'pet': 'cat'}
## NEVER DO THIS
# This is how to mess up the graph
g.node[6] = 'psych'
# The node exists, but are there underlying problems I'm not aware of?
print(g.nodes()) # [1, 5, 6]
# Here's the first problem. This should be a dict, but it's a str
print(type(g.node[6])) # <class 'str'>
# This error occurs because of the abuse of the API
#g.add_node(6) # AttributeError: 'str' object has no attribute 'update'
# This is how to "correctly" add a node via <Graph>.node, but never do this
g.node[6] = {'psych': 'psych'}
g.add_node(6)
print(g.nodes()) # [1, 5, 6]
def get_edges():
'''<Graph>.edges() returns a Python list of tuples, where each 2-tuple represents an edge between two nodes'''
g = Graph([(1, 5), (5, 5)])
#print(type(g.edges())) # <class 'list'>
#print(g.edges()) # [(1, 5), (5, 5)]
# Iterate over 2-tuples
for e in g.edges():
print(e) # (1, 5)\n(5, 5)
def add_edges():
'''Including an arbitrary attribute with newly added edges will add that attribute to all of the new edges'''
g = Graph([(1, 5), (5, 5)])
g.add_edges_from([[4, 6], (7, 8)], win='yes')
print(g.nodes()) # [1, 5, 4, 6, 7, 8]
print(g.edges()) # [(1, 5), (5, 5), (4, 6), (7, 8)]
print(
g.edge
) # {1: {5: {}}, 5: {1: {}, 5: {}}, 4: {6: {'win': 'yes'}}, 6: {4: {'win': 'yes'}}, 7: {8: {'win': 'yes'}}, 8: {7: {'win': 'yes'}}}
def create_graph_from_edges():
'''
- Don't use this strategy alone to copy a graph
- None of the arbitrary attributes from nodes, edges, or the graph are copied
- When a new graph is created from the edges of an existing graph, the nodes that form each edge are also created
- Thus, creating a copy from edges is almost a true copy
- It is NOT a true copy because any nodes without edges are not copied!
'''
g = Graph([(1, 5), (5, 5)])
g.add_node(6)
g.edge[1][5]['foo'] = 'bar'
print(g.edge[1][5]) # {'foo': 'bar'}
print(g.nodes()) # [1, 5, 6]
h = Graph()
# Yes, this is the required syntax to do this
h.add_edges_from(g.edges())
print(h.edge[1][5]) # {}
print(h.nodes()) # [1, 5]
print(h.edges()) # [(1, 5), (5, 5)]
def create_graph_from_graph():
'''Passing another graph object appears to have the same net result as <Graph>.copy()'''
g = Graph([(1, 5), (5, 5)])
g.add_node(6)
h = Graph(g)
print(h.nodes()) # [1, 5, 6]
print(h.edges()) # [(1, 5), (5, 5)]
g.node[1]['color'] = 'black'
print(g.node[1]) # {'color': 'black'}
print(h.node[1]) # {}
def create_graph_from_nodes():
'''
The net result is the same as in v1.11: the new graph gets all new nodes that are copies of the original nodes
- No edges are copied
- No arbitrary attributes are copied
'''
g = Graph([(1, 5), (5, 5)])
g.graph['baz'] = 'boo'
g.add_node(6)
print(g.nodes()) # [1, 5, 6]
print(g.edges()) # [(1, 5), (5, 5)]
g.nodes[5]['foo'] = 'bar'
print(g.nodes[5]) # {'foo': 'bar'}
h = Graph()
h.add_nodes_from(g)
print(h.graph) # {}
print(h.nodes()) # [1, 5, 6]
print(h.edges()) # {}
print(h.nodes[5]) # {}
def create_graph_from_nodes():
'''
- Don't use this strategy alone to copy a graph
- None of the arbitrary attributes from nodes, edges, or the graph are copied
- If the nodes of a graph object are used to create a new graph object:
- No edges are created in the new graph.
'''
g = Graph([(1, 5), (5, 5)])
g.graph['baz'] = 'boo'
g.add_node(6)
print(g.nodes()) # [1, 5, 6]
print(g.edges()) # [(1, 5), (5, 5)]
g.node[5]['foo'] = 'bar'
print(g.node[5]) # {'foo': 'bar'}
h = Graph()
h.add_nodes_from(g)
print(h.graph) # {}
print(h.nodes()) # [1, 5, 6]
print(h.edges()) # {}
print(h.node[5]) # {}
def construct(G: Graph, weight="weight"):
e_weight = {}
adj, radj = {}, {}
edges = G.edges()
for e in edges:
e_weight[e] = edges[e][weight]
if e[0] not in adj:
adj[e[0]] = []
adj[e[0]].append(e[1])
if e[1] not in radj:
radj[e[1]] = []
radj[e[1]].append(e[0])
return e_weight, [adj, radj]
def examine_node_attributes():
'''
The v2.4 API is slightly different because it uses <Graph>.nodes (or <Graph>.nodes()) while <Graph>.node doesn't exist
- Even though the NodeView is new, the underlying Python dicts that store attributes are the same as v1.11
'''
g = Graph([(1, 5), (5, 5)])
g.add_node(5)
print(g.nodes()) # [1, 5]
print(g.edges()) # [(1, 5), (5, 5)]
#print(g.node[5]) # AttributeError: 'Graph' object has no attribute 'node'
print(g.nodes[5]) # {}
g.nodes[5]['foo'] = 'bar'
print(g.nodes[5]) # {'foo': 'bar'}
def create_graph_with_new_data():
'''
- Parallel edges are not allowed
- The data can be:
- An edge list
- Any NetworkX graph object
- The data cannot be a flat list of nodes!
- It can't be a list of nodes because a bunch of unconnected nodes don't compose a very interesting graph
- Nodes can be any hashable object. Recall that immutable objects are implicitly hashable: int, string, tuple, etc.
'''
# Create with edge list. Since this is an undirected graph, there is only one edge between 1 and 3
g = Graph([(1, 'foo'), (1, 3), (3, 1)])
g.add_node(6)
# Create with another graph
print(g.nodes()) # [1, 'foo', 3, 6]
print(g.edges()) # [(1, 'foo'), (1, 3)]