import gmsh
import sys

gmsh.initialize(sys.argv)
gmsh.model.add("square")
gmsh.model.geo.addPoint(0, 0, 0, 0.1, 1)
gmsh.model.geo.addPoint(1, 0, 0, 0.1, 2)
gmsh.model.geo.addPoint(1, 1, 0, 0.1, 3)
gmsh.model.geo.addPoint(0, 1, 0, 0.1, 4)
gmsh.model.geo.addLine(1, 2, 1)
gmsh.model.geo.addLine(2, 3, 2)
gmsh.model.geo.addLine(3, 4, 3)
# try automatic assignement of tag
line4 = gmsh.model.geo.addLine(4, 1)
gmsh.model.geo.addCurveLoop([1, 2, 3, line4], 1)
gmsh.model.geo.addPlaneSurface([1], 6)
gmsh.model.geo.synchronize()
gmsh.model.mesh.generate(2)
gmsh.write("square.msh")
gmsh.finalize()