Field maps contain a ton if information so they're a bit of a handful when you try to make them from scratch in python. To get your own code, you can perform a spatial join using the tool in ArcCatalog with the field map exactly like you want it, then open the Geoprocessor's Results dialog and copy the field map string from there. Here's some code that I built with that as a starting point.
FieldMapString = "" \
+ """AddressNumber "AddressNumber" true true false 4 Long 0 10 ,First,#,""" + AddressFC+ """,AddressNumber,-1,-1;"""\
+ """AddressNumberFraction "AddressNumberFraction" true true false 3 Text 0 0 ,First,#,""" + AddressFC+ """,AddressNumberFraction,-1,-1;"""\
+ """PreDirection "PreDirection" true true false 2 Text 0 0 ,First,#,""" + AddressFC+ """,PreDirection,-1,-1;"""\
+ """PreType "PreType" true true false 20 Text 0 0 ,First,#,""" + AddressFC+ """,PreType,-1,-1;"""\
+ """CoreStreetName "CoreStreetName" true true false 20 Text 0 0 ,First,#,""" + AddressFC+ """,CoreStreetName,-1,-1;"""\
+ """PostType "PostType" true true false 20 Text 0 0 ,First,#,""" + AddressFC+ """,PostType,-1,-1;"""\
+ """PostDirection "PostDirection" true true false 2 Text 0 0 ,First,#,""" + AddressFC+ """,PostDirection,-1,-1;"""\
+ """PostModifier "PostModifier" true true false 10 Text 0 0 ,First,#,""" + AddressFC + """,PostModifier,-1,-1;"""\
+ """PostalCity "PostalCity" true true false 15 Text 0 0 ,First,#,""" + AddressFC+ """,PostalCity,-1,-1;"""\
+ """SubUnitType "SubUnitType" true true false 15 Text 0 0 ,First,#,""" + AddressFC+ """,SubUnitType,-1,-1;"""\
+ """SubUnitIdentifier "SubUnitIdentifier" true true false 10 Text 0 0 ,First,#,""" + AddressFC+ """,SubUnitIdentifier,-1,-1;"""\
+ """AddressPointID "AddressPointID" true true false 4 Long 0 10 ,First,#,""" + AddressFC+ """,AddressPointID,-1,-1;"""\
+ """PointIssue "PointIssue" true true false 2 Short 0 5 ,First,#,""" + AddressFC+ """,PointIssue,-1,-1;"""\
+ """AddressChange "AddressChange" true true false 2 Short 0 5 ,First,#,""" + AddressFC+ """,AddressChange,-1,-1;"""\
+ """ParcelException "ParcelException" true true false 2 Short 0 5 ,First,#,""" + AddressFC+ """,ParcelException,-1,-1;"""\
+ """PARCEL "PARCEL" true true false 50 Text 0 0 ,First,#,""" + ParcelFC+ """,PARCEL,-1,-1;"""\
+ """ADDRESS "ADDRESS" true true false 60 Text 0 0 ,First,#,""" + ParcelFC+ """,ADDRESS,-1,-1;"""\
+ """CITY_STATE "CITY_STATE" true true false 41 Text 0 0 ,First,#,""" + ParcelFC+ """,CITY_STATE,-1,-1;"""\
+ """PROPADDNUM "PROPADDNUM" true true false 10 Text 0 0 ,First,#,""" + ParcelFC+ """,PROPADDNUM,-1,-1;"""\
+ """PROPPREDIR "PROPPREDIR" true true false 2 Text 0 0 ,First,#,""" + ParcelFC+ """,PROPPREDIR,-1,-1;"""\
+ """PROPSTNM "PROPSTNM" true true false 25 Text 0 0 ,First,#,""" + ParcelFC+ """,PROPSTNM,-1,-1;"""\
+ """PROPSTTYPE "PROPSTTYPE" true true false 10 Text 0 0 ,First,#,""" + ParcelFC+ """,PROPSTTYPE,-1,-1;"""\
+ """PROPPOST "PROPPOST" true true false 2 Text 0 0 ,First,#,""" + ParcelFC+ """,PROPPOST,-1,-1;"""\
+ """PROPUNIT "PROPUNIT" true true false 10 Text 0 0 ,First,#,""" + ParcelFC+ """,PROPUNIT,-1,-1;"""\
+ """PROPUNUM "PROPUNUM" true true false 10 Text 0 0 ,First,#,""" + ParcelFC+ """,PROPUNUM,-1,-1;"""
fieldmappings = arcpy.FieldMappings()
fieldmappings.loadFromString(FieldMapString)
arcpy.SpatialJoin_analysis(AddressFC, ParcelFC, SpatialJoinFC, "JOIN_ONE_TO_MANY", "KEEP_COMMON", fieldmappings)