Why is this python script not working?

Question

import bmesh
bmesh.from_edit_mesh(bpy.context.edit_object.data).faces[1].select=True

It says python script fail
What should I do ?

Answer 1

Background

This is how to create a new object and add the vertices in the verts list:

import bpy
import bmesh

verts = [(1, 1, 1), (0, 0, 0)]  # 2 verts made with XYZ coords
mesh = bpy.data.meshes.new("mesh")  # add a new mesh
obj = bpy.data.objects.new("MyObject", mesh)  # add a new object using the mesh

scene = bpy.context.scene
scene.objects.link(obj)  # put the object into the scene (link)
scene.objects.active = obj  # set as the active object in the scene
obj.select = True  # select object

mesh = bpy.context.object.data
bm = bmesh.new()

for v in verts:
    bm.verts.new(v)  # add a new vert

# make the bmesh the object's mesh
bm.to_mesh(mesh)  
bm.free()  # always do this when finished

This is how to alter an existing mesh:

import bpy
import bmesh

verts = [(1, 1, 1), (0, 0, 0)]  # 2 verts made with XYZ coords
mesh = bpy.context.object.data
bm = bmesh.new()

# convert the current mesh to a bmesh
bm.from_mesh(mesh)

for v in verts:
    bm.verts.new(v)  # add a new vert

# make the bmesh the object's mesh
bm.to_mesh(mesh)  
bm.free()  # always do this when finished

Answer

As for selection:

import bpy
import bmesh

mesh = bpy.context.object.data
bm = bmesh.new()

# convert the current mesh to a bmesh
bm.from_mesh(mesh)

# must run this so we can use indexing on the faces
bm.faces.ensure_lookup_table()

# "select" the 0th face by setting its select property to True
bm.faces[0].select = True

# make the bmesh the object's mesh
bm.to_mesh(mesh)  
bm.free()  # always do this when finished

# go back to edit mode to see the selection
bpy.ops.object.mode_set(mode='EDIT')

To test this:

1. Add a cube (go into edit mode and deselect all faces)
2. Paste the script into Blender's text editor
3. Hit run script in the text editor with the cube object still selected