python numbers

print '-'*60

n = 0.387951

print n                             # 0.387951

print round(n, 3)                   # 0.388
print format(n, '.18f')             # 0.387950999999999990
print n*0.000001                    # 3.87951e-07
print format(n*0.000001, '.18f')    # 0.000000387951000000
print '%.8f' % n                    # 0.38795100
print '%.10f' % n                   # 0.3879510000
print '%.12f' % n                   # 0.387951000000
print '%.14f' % n                   # 0.38795100000000
print '%.16f' % n                   # 0.3879510000000000    <- sechzehnte Nachkommastelle noch "in Orndung"
print '%.17f' % n                   # 0.38795099999999999   <- ab siebzehnter Nachkommastelle faellt die Abweichung auf
print '%.18f' % n                   # 0.387950999999999990


print n                             # 0.387951 <- n ist nach wie vor unveraendert



print '-'*60

n = 0.1

print n                             # 0.1

print round(n, 3)                   # 0.1
print format(n, '.18f')             # 0.100000000000000006
print n*0.000001                    # 1e-07
print format(n*0.000001, '.18f')    # 0.000000100000000000
print '%.8f' % n                    # 0.10000000
print '%.10f' % n                   # 0.1000000000
print '%.12f' % n                   # 0.100000000000
print '%.14f' % n                   # 0.10000000000000
print '%.16f' % n                   # 0.1000000000000000    <- sechzehnte Nachkommastelle noch "in Orndung"
print '%.17f' % n                   # 0.10000000000000001   <- ab siebzehnter Nachkommastelle faellt die Abweichung auf
print '%.18f' % n                   # 0.100000000000000006


print '-'*60

a, b, c = 0.1, 0.1, 0.1

print a + b + c                     # 0.3
print a + b + c == 0.3              # False
print '%.16f' % a                   # 0.1000000000000000
print '%.17f' % a                   # 0.10000000000000001
print '%.17f' % (a+b+c)             # 0.30000000000000004



print '-'*60

import decimal
from decimal import Decimal, Context

print Decimal(0.1)                  # 0.1000000000000000055511151231257827021181583404541015625
print Decimal('0.1')                # 0.1

a = Decimal('0.1')
b = Decimal('0.1')
c = Decimal('0.1')

print a + b + c == Decimal('0.3')   # True
print a + b + c == 0.3              # False

print format(Decimal('0.1'), '.20f')    # 0.10000000000000000000
print format(Decimal(0.1), '.20f')      # 0.10000000000000000555