Lo que todo programador debería saber sobre aritmética de punto flotante
Add Python cheatsheet.
authored by
Juanjo Conti
and committed by
Michael Borgwardt
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content/languages/python.html
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content/languages/python.html
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---
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title: Floating-point cheat sheet for Python
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description: Tips for using floating-point and decimal numbers in Python
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---
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Floating-Point Types
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--------
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Almost all platforms map Python floats to [IEEE 754](/formats/fp/)
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double precision.
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f = 0.1
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Decimal Types
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-------------
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Python has an [arbitrary-precision](/formats/exact/) decimal type named <code>Decimal</code> in the <code>decimal</code> module, which
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also allows to choose the [rounding mode](/errors/rounding/).
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a = Decimal('0.1')
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b = Decimal('0.2')
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c = a + b # returns a Decimal representing exactly 0.3
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How to Round
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------------
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To get a string:
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"%.2f" % 1.2399 # returns "1.24"
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"%.3f" % 1.2399 # returns "1.240"
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"%.2f" % 1.2 # returns "1.20"
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To print to standard output:
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print "%.2f" % 1.2399 # just use print and string formatting
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If you need a specific [rounding mode](/errors/rounding/) and other parameters can be defined in a Context object:
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getcontext().prec = 7
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Resources
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---------
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* [Floating Point Arithmetic: Issues and Limitations](http://docs.python.org/tutorial/floatingpoint.html)
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* [The decimal module](http://docs.python.org/library/decimal.html)
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* [Context objects](http://docs.python.org/library/decimal.html#context-objects)
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* [String formatting in Python](http://docs.python.org/library/stdtypes.html#string-formatting-operations)