pango.FontFace — an object representing a group of fonts varying only in size.
A pango.FontFace
object represents a group of fonts with the same family, weight, slant,
stretch and width but varying sizes. A list of font faces can be retrieved
from a pango.FontFamily 
object using the pango.FontFamily.list_faces() 
method.
    def describe()| Returns : | a pango.FontDescriptionobject containing the description of the face. | 
The describe() method returns a pango.FontDescription 
object containing the family, style, variant, weight and stretch of the
pango.FontFace.
The size attribute field will be unset.
    def get_face_name()| Returns : | the face name for the face. | 
The get_face_name() method returns a
string representing this font face. This name is unique among all faces in the
family and is suitable for displaying to users.
    def list_sizes()| Returns : | a tuple containing a list of face sizes in
	  pango units or None | 
This method is available in PyGTK 2.4 and above.
The list_sizes() method returns a tuple
containing the available sizes for a bitmap font. If the font face is a
scalable font this method returns None.