Significant figures in the decimal module

from decimal import Decimal
>>> Decimal('1.0') + Decimal('2.0')
Decimal("3.0")

>>> Decimal('1.00') / Decimal('3.00')
Decimal("0.3333333333333333333333333333")

decimal.getcontext().prec=2

decimal.getcontext().prec=2

>>> "%8.2e"%  ( 1.0/3.0 )
'3.33e-01'

def lround(x,leadingDigits=0):
    """Return x either as 'print' would show it (the default)
    or rounded to the specified digit as counted from the leftmost
    non-zero digit of the number, e.g. lround(0.00326,2) --> 0.0033
    """
    assert leadingDigits>=0
    if leadingDigits==0:
            return float(str(x)) #just give it back like 'print' would give it
    return float('%.*e' % (int(leadingDigits),x)) #give it back as rounded by the %e format

>>> lround(1./3.,2),str(lround(1./3.,2)),str(lround(1./3.,4))
(0.33000000000000002, '0.33', '0.3333')