<｜begin▁of▁sentence｜>### Instruction:
As a network analyst, you are tasked with creating a visual representation of a network graph. The graph consists of vertices connected by edges, and you need to draw a diamond shape at each vertex position. Furthermore, the resulting visualization needs to be saved as a PNG file for future reference and sharing. Utilizing the `draw_path` method from the `DiamondDrawer` in the `igraph` API can help accomplish this task. This approach enables you to illustrate the network structure while highlighting the vertex positions with diamond shapes.
### Response:
import igraph as ig
import cairo

# Create a graph
edges = [(0, 1), (1, 2), (2, 3), (3, 0)]
g = ig.Graph(edges=edges)

# Define the layout for the graph
layout = g.layout('kk')  # Kamada-Kawai layout

# Define the size of the image
width, height = 300, 300

# Create a Cairo Image Surface to draw on
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
ctx = cairo.Context(surface)

# Define the size of the shape to be drawn
shape_width = 20
shape_height = 20

# Draw shapes at vertex positions
for vertex_id in range(g.vcount()):
    center_x, center_y = layout[vertex_id]
    ig.drawing.shapes.DiamondDrawer.draw_path(ctx, center_x, center_y, shape_width, shape_height)
    ctx.stroke()  # Stroke the path without filling

# Save the graph with customized vertex shapes to a PNG file
surface.write_to_png('graph_with_custom_shapes.png')
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