{"id":2281,"date":"2021-02-26T06:04:05","date_gmt":"2021-02-26T06:04:05","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=2281"},"modified":"2021-02-26T06:08:24","modified_gmt":"2021-02-26T06:08:24","slug":"python-decimal","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/advanced-python\/python-decimal\/","title":{"rendered":"Python Decimal"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about the Python decimal<\/code> module that supports fast correctly-rounded decimal floating-point arithmetic.<\/p>\n\n\n\n

Introduction to the Python decimal module #<\/a><\/h2>\n\n\n\n

Many decimal numbers don’t have exact representations in binary floating-point<\/a> such as 0.1. When using these numbers in arithmetic operations, you’ll get a result that you would not expect. For example:<\/p>\n\n\n

x = 0.1<\/span>\ny = 0.1<\/span>\nz = 0.1<\/span>\n\ns = x + y + z\n\nprint<\/span>(s)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
0.30000000000000004<\/span><\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\n
The result is 0.30000000000000004, not 0.3.<\/p>\n\n\n\n
To solve this problem, you use the Decimal<\/code> class from the decimal<\/code> module as follows:<\/p>\n\n\n
import<\/span> decimal\nfrom<\/span> decimal import<\/span> Decimal\n\n\nx = Decimal('0.1'<\/span>)\ny = Decimal('0.1'<\/span>)\nz = Decimal('0.1'<\/span>)\n\ns = x + y + z\n\nprint(s)<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
0.3<\/span><\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\n
The output is as expected.<\/p>\n\n\n\n
The Python decimal<\/code> module supports arithmetic that works the same as the arithmetic you learn at school.<\/p>\n\n\n\n
Decimal('0.1'<\/span>) + Decimal('0.1'<\/span>) + Decimal('0.1'<\/span>) - Decimal('0.3'<\/span>)<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Decimal context #<\/a><\/h2>\n\n\n\n
Decimal always associates with a context<\/a> that controls the following aspects:<\/p>\n\n\n\n
Unlike floats<\/a>, Python represents decimal numbers exactly. And the exactness carries over into arithmetic. For example, the following expression returns exactly 0.0:<\/p>\n\n\n