1 | initial version |

The output of a command like `graphs.planar_graphs(4)`

is an iterator
that can yield all planar graphs with the specified number of vertices.

To get the documentation, do one of the following:

in Sage, type

`graphs.planar_graph?`

and hit the return or enter key.This will display the documentation for this function, in text mode.

in Sage, type

`graphs.planar_graph??`

and hit the return or enter key.This will display the code source for this function, including the documentation string.

in Sage, type

`browse_sage_doc(graphs.planar_graph)`

.This will open the documentation for this function, in html, in a browser tab.

browse the online documentation:

So for example, if you define

```
sage: gen = graphs.planar_graphs(n)
```

and turn it into a list

```
sage: G = list(gen)
```

you could display a summary of this list of graphs and their diameters:

```
sage: newline = '\n'
sage: s = 'There are {} planar graphs on {} vertices.'
sage: s = s.format(n, len(G))
sage: for j, g in enumerate(G):
....: s += newline + '{}.'.format(j)
....: s += newline + 'Edges: {}'.format(g.edges(labels=False))
....: s += newline + 'Diameter: {}'.format(g.diameter())
....:
sage: print(s)
There are 4 planar graphs on 6 vertices.
0.
Edges: [(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)]
Diameter: 1
1.
Edges: [(1, 2), (1, 3), (2, 3), (2, 4), (3, 4)]
Diameter: 2
2.
Edges: [(1, 2), (1, 3), (2, 4), (3, 4)]
Diameter: 2
3.
Edges: [(1, 2), (2, 3), (2, 4), (3, 4)]
Diameter: 2
4.
Edges: [(1, 2), (2, 3), (3, 4)]
Diameter: 3
5.
Edges: [(1, 2), (2, 3), (2, 4)]
Diameter: 2
```

or plot them all:

```
sage: for g in G:
....: plot(g)
....:
Launched png viewer for Graphics object consisting of 11 graphics primitives
Launched png viewer for Graphics object consisting of 10 graphics primitives
Launched png viewer for Graphics object consisting of 9 graphics primitives
Launched png viewer for Graphics object consisting of 9 graphics primitives
Launched png viewer for Graphics object consisting of 8 graphics primitives
Launched png viewer for Graphics object consisting of 8 graphics primitives
```

etc.

Don't hesitate to suggest any specific improvement to the documentation.

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