pyopengl set multipass texture blending mode

Question

im trying to get multi texturing working and have so far got miltiple textures to load using this function

def loadTexture(name):

    img = PIL.Image.open(name) # .jpg, .bmp, etc. also work
    img_data = numpy.array(list(img.getdata()), numpy.int8)

    id = glGenTextures(1)
    glPixelStorei(GL_UNPACK_ALIGNMENT,1)
    glBindTexture(GL_TEXTURE_2D, id)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img.size[0], img.size[1], 0, GL_RGB, GL_UNSIGNED_BYTE, img_data)
    return id

And I can set the texture to use with this code

glBindTexture(GL_TEXTURE_2D, 1)
glEnable(GL_TEXTURE_2D)

My first attempt has been this:

glBindTexture(GL_TEXTURE_2D, 1)
glEnable(GL_TEXTURE_2D)
glBegin(GL_TRIANGLES)
....
glEnd()

glBindTexture(GL_TEXTURE_2D, 3)
glEnable(GL_TEXTURE_2D)
glBegin(GL_TRIANGLES)
....
glEnd()

So i render the polys twice and select a different texture each time, this seems to work in as much as calling glBindTexture(GL_TEXTURE_2D, n) will select the relivant texture and it will render but there is no blending going on per se, i just see the last selected texture in the render. I've tried adding glEnable(GL_BLEND), but that doesn't seem to do anything.

What I would like to do is to add pixels of the two passes together

How would I go about this?