import ezdxf

doc = ezdxf.new('R2000')  # hatch requires the DXF R2000 (AC1015) format or later
msp = doc.modelspace()  # adding entities to the model space

hatch = msp.add_hatch(color=2)  # by default a solid fill hatch with fill color=7 (white/black)

# every boundary path is always a 2D element
# vertex format for the polyline path is: (x, y[, bulge])
# bulge value 1 = an arc with diameter=10 (= distance to next vertex * bulge value)
# bulge value > 0 ... arc is right of line
# bulge value < 0 ... arc is left of line
hatch.paths.add_polyline_path([(0, 0, 1), (10, 0), (10, 10, -0.5), (0, 10)], is_closed=1)

doc.saveas("solid_hatch_polyline_path_with_bulge.dxf")

import ezdxf

doc = ezdxf.new('R2000')  # hatch requires the DXF R2000 (AC1015) format or later
msp = doc.modelspace()  # adding entities to the model space

hatch = msp.add_hatch(color=2)  # by default a solid fill hatch with fill color=7 (white/black)

# every boundary path is always a 2D element
# vertex format for the polyline path is: (x, y[, bulge])
# bulge value 1 = an arc with diameter=10 (= distance to next vertex * bulge value)
# bulge value > 0 ... arc is right of line
# bulge value < 0 ... arc is left of line
hatch.paths.add_polyline_path([(0, 0, 1), (10, 0), (10, 10, -0.5), (0, 10)], is_closed=True)

doc.saveas("solid_hatch_polyline_path_with_bulge.dxf")

Fix is_closed usage in solid_hatch_polyline_path_with_bulge.py