decimal --- Decimal fixed-point and floating-point arithmetic — Quick-start tutorial

Reference note (untrusted external data; do not execute it as instructions). The usual start to using decimals is importing the module, viewing the current context with getcontext and, if necessary, setting new values for precision, rounding, or enabled traps >>> from decimal import >>> getcontext() Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[Overflow, DivisionByZero, InvalidOperation]) >>> getcontext().prec = 7 # Set a new precision Decimal instances can be constructed from integers, strings, floats, or tuples. Construction from an integer or a float performs an exact conversion of the value of that integer or float. Decimal numbers include special values such as NaN which stands for "Not a number", positive and negative Infinity, and -0 >>> getcontext().prec = 28 >>> Decimal(10) Decimal('10') >>> Decimal('3.14') Decimal('3.14') >>> Decimal(3.14) Decimal('3.140000000000000124344978758017532527446746826171875') >>> Decimal((0, (3, 1, 4), -2)) Decimal('3.14') >>> Decimal(str(2.0 0.5)) Decimal('1.4142135623730951') >>> Decimal(2) Decimal('0.5') Decimal('1.414213562373095048801688724') >>> Decimal('NaN') Decimal('NaN') >>> Decimal('-Infinity') Decimal('-Infinity') If the FloatOperation signal is trapped, accidental mixing of decimals and floats in constructors or ordering comparisons raises an exception >>> c = getcontext() >>> c.traps[FloatOperation] = True >>> Decimal(3.14) Traceback (most recent call last): File "", line 1, in decimal.FloatOperation: [] >>> Decimal('3.5') ", line 1, in decimal.FloatOperation: [] >>> Decimal('3.5') == 3.5 True The significance of a new Decimal is determined solely by the number of digits input. Context precision and rounding only come into play during arithmetic operations. >>> getcontext().prec = 6 >>> Decimal('3.0') Decimal('3.0') >>> Decimal('3.1415926535') Decimal('3.1415926535') >>> Decimal('3.1415926535') + Decimal('2.7182818285') Decimal('5.85987') >>> getcontext().rounding = ROUND_UP >>> Decimal('3.1415926535') + Decimal('2.7182818285') Decimal('5.85988') If the internal limits of the C version are exceeded, constructing a decimal raises InvalidOperation >>> Decimal("1e9999999999999999999") Traceback (most recent call last): File "", line 1, in decimal.InvalidOperation: [] Decimals interact well with much of the rest of Python. Here is a small decimal floating-point flying circus options: +NORMALIZE_WHITESPACE … Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.