#
#  Record name, orbital position, radius in km.
#
sun =     [ 'Sun',     0, 696000.0 ]
mercury = [ 'Mercury', 1,   1516.0 ]
venus =   [ 'Venus',   2,   3760.4 ]
earth =   [ 'Earth',   3,   3963.1 ]
mars =    [ 'Mars',    4,   2106.1 ]
#
#  Print one of the planets.
#
print ( '' )
print ( '  Data for venus:' )
print ( venus )
#
#  Create a list of lists.
#
solar = [ sun, mercury, venus, earth, mars ]
print ( '' )
print ( '  Data for solar system' )
print ( solar )
#
#  Print radius of each item.
#
for planet in solar:
  print ( planet[0], ' Radius = ', planet[2] )
#
#  Add density in kg/m^3.
#
sun.append ( 1408.0 )
mercury.append ( 5429.0 )
venus.append ( 5243.0 )
earth.append ( 5514.0 )
mars.append ( 3934.0 )
print ( '' )
print ( '  Add density for each.  Here is updated sun:' )
print ( sun )
#
#  By updating individual planets, we also update the full solar list.
#
print ( '' )
print ( '  The solar list is automatically updated.' )
print ( solar )
#
#  Sort data by radius.
#
solar_sorted = sorted ( solar, key = lambda planet : planet[2] )
print ( '' )
print ( '  Sorted by radius' )
print ( solar_sorted )
#
#  Change radius of Mars.  Directly, or through solar?
#
solar[4][2] = 99.0
print ( '' )
print ( '  Change radius of solar[4][2].  Does this update Mars record?' )
print ( mars )
print ( solar )
#
#  Create planet Fred.  Add to solar.
#
print ( '' )
print ( '  Create planet Fred, add to solar.' )
fred = [ 'Fred', 9, 1234.0, 5678.0 ]
solar.append ( fred )
print ( solar )