Editing Python (programming language) (section)

===Arithmetic operations===
Python includes conventional symbols for arithmetic operators (<code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>), the floor-division operator <code>//</code>, and the [[modulo operation|modulo operator]] <code>%</code>. (With the module operator, a remainder can be negative,<!--unlike in C language depending on compiler,<ref>{{Cite web|url=https://stackoverflow.com/questions/11720656/modulo-operation-with-negative-numbers/42131603|title=c – Modulo operation with negative numbers|quote=Note that, in C89, whether the result round upward or downward is implementation-defined.|website=Stack Overflow|access-date=25 September 2019}}</ref>--> e.g., <code>4 % -3 == -2</code>.) Python also offers the <code>**</code> symbol for [[exponentiation]], e.g. <code>5**3 == 125</code> and <code>9**0.5 == 3.0</code>; it also offers the matrix‑multiplication operator <code>@</code> .<ref>{{cite web |url=https://legacy.python.org/dev/peps/pep-0465/ |title=PEP 465 – A dedicated infix operator for matrix multiplication |work=python.org |access-date=3 July 2018 |archive-date=29 May 2020 |archive-url=https://web.archive.org/web/20200529200310/https://legacy.python.org/dev/peps/pep-0465/ |url-status=live}}</ref> These operators work as in traditional mathematics; with the same [[order of operations|precedence rules]], the [[infix notation|infix]] operators <code>+</code> and <code>-</code> can also be [[unary operation|unary]], to represent positive and negative numbers respectively.

Division between integers produces floating-point results. The behavior of division has changed significantly over time:<ref name="pep0238"/>
* The current version of Python (i.e., since 3.0) changed <code>the /</code> operator to always represent floating-point division, e.g., {{code|class=nowrap|2=python|1=5/2 == 2.5}}.
* The floor division <code>//</code> operator was introduced. Thus <code>7//3 == 2</code>, <code>-7//3 == -3</code>, <code>7.5//3 == 2.0</code>, and <code>-7.5//3 == -3.0</code>. For outdated Python 2.7 adding the {{code|class=nowrap|2=python2|1=from __future__ import division}} statement causes a module in Python 2.7 to use Python&nbsp;3.0 rules for division instead (see above).

In Python terms, the <code>/</code> operator represents ''true division'' (or simply ''division''), while the <code>//</code> operator represents ''floor division.'' Before version 3.0, the <code>/</code> operator represents ''classic division''.<ref name="pep0238"/>

[[Rounding]] towards negative infinity, though a different method than in most languages, adds consistency to Python. For instance, this rounding implies that the equation {{code|class=nowrap|2=python|1=(a + b)//b == a//b + 1}} is always true. The rounding also implies that the equation {{code|class=nowrap|2=python|1=b*(a//b) + a%b == a}} is valid for both positive and negative values of <code>a</code>. As expected, the result of <code>a%b</code> lies in the [[half-open interval]] [0, ''b''), where <code>b</code> is a positive integer; however, maintaining the validity of the equation requires that the result must lie in the interval (''b'', 0] when <code>b</code> is negative.<ref name="AutoNT-62"/>

Python provides a <code>round</code> function for rounding a float to the nearest integer. For [[Rounding#Tie-breaking|tie-breaking]], Python&nbsp;3 uses the ''round to even'' method: <code>round(1.5)</code> and <code>round(2.5)</code> both produce <code>2</code>.<ref name="AutoNT-64"/> Python versions before 3 used the [[Rounding#Rounding away from zero|round-away-from-zero]] method: <code>round(0.5)</code> is <code>1.0</code>, and <code>round(-0.5)</code> is <code>−1.0</code>.<ref name="AutoNT-63"/>

Python allows Boolean expressions that contain multiple equality relations to be consistent with general usage in mathematics. For example, the expression <code>a < b < c</code> tests whether <code>a</code> is less than <code>b</code> and <code>b</code> is less than <code>c</code>.<ref name="AutoNT-65"/> C-derived languages interpret this expression differently: in C, the expression would first evaluate <code>a < b</code>, resulting in 0 or 1, and that result would then be compared with <code>c</code>.<ref name="CPL"/>

Python uses [[arbitrary-precision arithmetic]] for all integer operations. The <code>Decimal</code> type/class in the <code>decimal</code> module provides [[decimal floating point|decimal floating-point numbers]] to a pre-defined arbitrary precision with several rounding modes.<ref name="AutoNT-88"/> The <code>Fraction</code> class in the <code>fractions</code> module provides arbitrary precision for [[rational number]]s.<ref>{{cite web|title=What's New in Python 2.6 |url=https://docs.python.org/2.6/whatsnew/2.6.html|website=Python v2.6.9 documentation |date=Oct 29, 2013 |access-date=26 September 2015|archive-date=23 December 2019|archive-url=https://web.archive.org/web/20191223213856/https://docs.python.org/2.6/whatsnew/2.6.html|url-status=live}}</ref>

Due to Python's extensive mathematics library and the third-party library [[NumPy]], the language is frequently used for scientific scripting in tasks such as numerical data processing and manipulation.<ref>{{Cite web|url=https://www.stat.washington.edu/~hoytak/blog/whypython.html|title=10 Reasons Python Rocks for Research (And a Few Reasons it Doesn't) – Hoyt Koepke|website=University of Washington Department of Statistics |access-date=3 February 2019|archive-date=31 May 2020|archive-url=https://web.archive.org/web/20200531211840/https://www.stat.washington.edu/~hoytak/blog/whypython.html|url-status=dead}}</ref><ref>{{Cite web|url=https://engineering.ucsb.edu/~shell/che210d/python.pdf|title=An introduction to Python for scientific computing|last=Shell|first=Scott|date=17 June 2014|access-date=3 February 2019|archive-date=4 February 2019|archive-url=https://web.archive.org/web/20190204014642/https://engineering.ucsb.edu/~shell/che210d/python.pdf|url-status=live}}</ref>