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

> 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, capita

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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

&gt;&gt;&gt; from decimal import &gt;&gt;&gt; getcontext() Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[Overflow, DivisionByZero, InvalidOperation])

&gt;&gt;&gt; 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

&gt;&gt;&gt; getcontext().prec = 28 &gt;&gt;&gt; Decimal(10) Decimal('10') &gt;&gt;&gt; Decimal('3.14') Decimal('3.14') &gt;&gt;&gt; Decimal(3.14) Decimal('3.140000000000000124344978758017532527446746826171875') &gt;&gt;&gt; Decimal((0, (3, 1, 4), -2)) Decimal('3.14') &gt;&gt;&gt; Decimal(str(2.0 0.5)) Decimal('1.4142135623730951') &gt;&gt;&gt; Decimal(2) Decimal('0.5') Decimal('1.414213562373095048801688724') &gt;&gt;&gt; Decimal('NaN') Decimal('NaN') &gt;&gt;&gt; Decimal('-Infinity') Decimal('-Infinity')

If the FloatOperation signal is trapped, accidental mixing of decimals and floats in constructors or ordering comparisons raises an exception

&gt;&gt;&gt; c = getcontext() &gt;&gt;&gt; c.traps[FloatOperation] = True &gt;&gt;&gt; Decimal(3.14) Traceback (most recent call last): File "", line 1, in decimal.FloatOperation: [] &gt;&gt;&gt; Decimal('3.5') ", line 1, in decimal.FloatOperation: [] &gt;&gt;&gt; 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.

&gt;&gt;&gt; getcontext().prec = 6 &gt;&gt;&gt; Decimal('3.0') Decimal('3.0') &gt;&gt;&gt; Decimal('3.1415926535') Decimal('3.1415926535') &gt;&gt;&gt; Decimal('3.1415926535') + Decimal('2.7182818285') Decimal('5.85987') &gt;&gt;&gt; getcontext().rounding = ROUND_UP &gt;&gt;&gt; Decimal('3.1415926535') + Decimal('2.7182818285') Decimal('5.85988')

If the internal limits of the C version are exceeded, constructing a decimal raises InvalidOperation

&gt;&gt;&gt; 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 …

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