Planar code is for storing planar graphs. See https://houseofgraphs.org/help#format_pc.

I see that SageMath has a function called _read_planar_code, but I still don’t understand how to use it to read a graph file encoded with planar_code (this file may contain multiple graphs, for example, all 3-connected planar triangulations with 7-vertex).

s=graphs._read_planar_code("triangulations_10.pl")
s
next(s)

<generator object GraphGenerators._read_planar_code at 0x7f4ed1b099c0>

AttributeError Traceback (most recent call
last) Cell In[1], line 3
1 s=graphs._read_planar_code(“triangulations_10.pl”)
2 s
—-> 3 next(s)

File
/usr/lib/python3.12/site-packages/sage/graphs/graph_generators.py:1488,
in GraphGenerators.read_planar_code(self, code_input) 1433 r”””
1434 Returns a generator for the plane graphs in planar code format in
1435 the file code_input (see [BM2016]). (…) 1485 4: [1,
3, 2]} 1486 “”” 1487 # start of code to read planar code
-> 1488 header = code_input.read(15) 1489 assert header == ‘>>planar_code<<‘, ‘Not a valid planar code header’ 1491 # read
graph per graph

AttributeError: ‘str’ object has no attribute ‘read’

Actually, I want to iteratively read them and then filter out some graphs that satisfy certain properties, such as filtering out perfect graphs.

with open('planar_conn.7.g6', 'r') as file:
    for line in file:
        # Remove any leading/trailing whitespace
        graph6_string = line.strip()
        
        # Decode the graph6 string to a graph object
        graph = Graph(graph6_string)
        
        # Check if the graph meets the desired property (e.g., perfect graph)
        if graph.is_perfect():
            graph.show()
            break  # Stop reading further as the desired graph is found