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the tuple s elements are immutable the operator can be used to concatenate two tuples which does not directly modify their contents but produces a new tuple containing the elements of both for example given the variable t initially equal to 1 2 3 executing t t 4 5 first evaluates t 4 5 which yields 1 2 3 4 5 this result is then assigned back to t thereby effectively modifying the contents of t while conforming to the immutable nature of tuple objects parentheses are optional for tuples in unambiguous contexts 99 python features sequence unpacking where multiple expressions each evaluating to something assignable e g a variable or a writable property are associated just as in forming tuple literal as a whole the results are then put on the left hand side of the equal sign in an assignment statement this statement expects an iterable object on the right hand side of the equal sign to produce the same number of values as the writable expressions on the left hand side while iterating the statement assigns each of the values produced on the right to the corresponding expression on the left 100 python has a string format operator that functions analogously to printf format strings in the c language e g spam s eggs d blah 2 evaluates to spam blah eggs 2 in python 2 6 and 3 this operator was supplemented by the format method of the str class e g spam 0 eggs 1 format blah 2 python 3 6 added f strings spam blah eggs 2 f spam spam eggs eggs 101 strings in python can be concatenated by adding them using the same operator as for adding integers and floats e g spam eggs returns spameggs if strings contain numbers they are concatenated as strings rather than as integers e g 2 2 returns 22 python supports string literals in several ways delimited by single or double quotation marks single and double quotation marks have equivalent functionality unlike in unix shells perl and perl influenced languages both marks use the backslash as an escape character string interpolation became available in python 3 6 as formatted string literals 101 triple quoted i e starting and ending with three single or double quotation marks this may span multiple lines and function like here documents in shells perl and ruby raw string varieties denoted by prefixing the string literal with r escape sequences are not interpreted hence raw strings are useful where literal backslashes are common such as in regular expressions and windows style paths compare quoting in c python has array index and array slicing expressions in lists which are written as a key a start stop or a start stop step indexes are zero based and negative indexes are relative to the end slices take elements from the start index up to but not including the stop index the optional third slice parameter called step or stride allows elements to be skipped or reversed slice indexes may be omitted for example a returns a copy of the entire list each element of a slice is a shallow copy in python a distinction between expressions and statements is rigidly enforced in contrast to languages such as common lisp scheme or ruby this distinction leads to duplicating some functionality for example list comprehensions vs for loops conditional expressions vs if blocks the eval vs exec built in functions in python 2 exec is a statement the former function is for expressions while the latter is for statements a statement cannot be part of an expression because of this restriction expressions such as list and dict comprehensions and lambda expressions cannot contain statements as a particular case an assignment statement such as a 1 cannot be part of the conditional expression of a conditional statement typing the standard type hierarchy in python 3 python uses duck typing and it has typed objects but untyped variable names type constraints are not checked at definition time rather operations on an object may fail at usage time indicating that the object is not of an appropriate type despite being dynamically typed python is strongly typed forbidding operations that are poorly defined e g adding a number and a string rather than quietly attempting to interpret them python allows programmers to define their own types using classes most often for object oriented programming new instances of classes are constructed by calling the class for example spamclass or eggsclass the classes are instances of the metaclass type which is an instance of itself thereby allowing metaprogramming and reflection before version 3 0 python had two kinds of classes both using the same syntax old style and new style 102 current python versions support the semantics of only the new style python supports optional type annotations 5 103 these annotations are not enforced by the language but may be used by external tools such as mypy to catch errors python includes a module typing including several type names for type annotations 104 105 also mypy supports a python compiler called mypyc which leverages type annotations for optimization 106 summary of python 3 s built in types type mutability description syntax examples bool immutable boolean value true false bytearray mutable sequence of bytes bytearray b some ascii bytearray b some ascii bytearray 119 105 107 105 bytes immutable sequence of bytes b some ascii b some ascii bytes 119 105 107 105 complex immutable complex number with real and imaginary parts 3 2 7 j 3 2 7 j 5 j dict mutable associative array or dictionary of key and value pairs can contain mixed types keys and values keys must be a hashable type key1 1 0 3 false types ellipsistype immutable an ellipsis placeholder to be used as an index in numpy arrays ellipsis float immutable 64 bit double precision floating point number ieee 754 number with 53 bits of precision in all supported versions since cpython 3 11 107 also in practice in 3 10 and older though technically there the precision is machine dependent 108 python s built in type memoryview does though support both 64 bit doubles and 32 bit floats and python s standard library struct module additionally supports 16 bit half floats python packages like numpy and pandas may also support 32 bit floats or more e g numpy half though support for half floats is often incomplete or non existent in most packages 109 16 bit bfloat has support in a few packages 110 most python implementations choose to support the double kind but some unusual subset implementations such as micropython for embedded programming support 32 bit ieee floats as their default float users can opt into 64 bit by setting micropy_float_impl to micropy_float_impl_double 1 33333 frozenset immutable unordered set contains no duplicates can contain mixed types if hashable frozenset 4 0 string true frozenset int immutable integer of unlimited magnitude 111 i e not using machine integers e g the python package numpy uses fixed sized integers for speedup and allows different sizes such as types numpy byte and numpy ulonglong all such types have a possibility of wrap around though less likely the larger it is 42 list mutable list can contain mixed types 4 0 string true types nonetype immutable an object representing the absence of a value often called null in other languages none types notimplementedtype immutable a placeholder that can be returned from overloaded operators to indicate unsupported operand types notimplemented range immutable an immutable sequence of numbers commonly used for iterating a specific number of times in for loops 112 range 1 10 range 10 5 2 set mutable unordered set contains no duplicates can contain mixed types if hashable 4 0 string true set str immutable a character string sequence of unicode codepoints wikipedia wikipedia spanning multiple lines tuple immutable tuple can contain mixed types 4 0 string true single element arithmetic operations python includes conventional symbols for arithmetic operators the floor division operator and the modulo operator with the modulo operator a remainder can be negative e g 4 3 2 python also offers the symbol for exponentiation e g 5 3 125 and 9 0 5 3 0 as well as the matrix multiplication operator 113 these operators work as in traditional mathematics with the same precedence rules the infix operators and can also be unary to represent positive and negative numbers respectively division between integers produces floating point results the behavior of division has changed significantly over time 114 the current version of python i e since 3 0 changed the operator to always represent floating point division e g 5 2 2 5 the floor division operator was introduced meaning that 7 3 2 7 3 3 7 5 3 2 0 and 7 5 3 3 0 for python 2 7 adding the from __future__ import division statement allows a module in python 2 7 to use python 3 x rules for division see above in python terms the operator represents true division or simply division while the operator represents floor division before version 3 0 the operator represents classic division 114 rounding towards negative infinity though a different method than in most languages adds consistency to python for instance this rounding implies that the equation a b b a b 1 is always true also the rounding implies that the equation b a b a b a is valid for both positive and negative values of a as expected the result of a b lies in the half open interval 0 b where b is a positive integer however maintaining the validity of the equation requires that the result must lie in the interval b 0 when b is negative 115 python provides a round function for rounding a float to the nearest integer for tie breaking python 3 uses the round to even method round 1 5 and round 2 5 both produce 2 116 python versions before 3 used the round away from zero method round 0 5 is 1 0 and round 0 5 is 1 0 117 python allows boolean expressions that contain multiple equality relations to be consistent with general usage in mathematics for example the expression a b c tests whether a is less than b and b is less than c 118 c derived languages interpret this expression differently in c the expression would first evaluate a b resulting in 0 or 1 and that result would then be compared with c 119 python uses arbitrary precision arithmetic for all integer operations the decimal type class in the decimal module provides decimal floating point numbers to a pre defined arbitrary precision with several rounding modes 120 the fraction class in the fractions module provides arbitrary precision for rational numbers 121 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 122 123 function syntax functions are created in python by using the def keyword a function is defined similarly to how it is called by first providing the function name and then the required parameters here is an example of a function that prints its inputs def printer input1 input2 already there print input1 print input2 printer hello example output hello already there to assign a default value to a function parameter in case no actual value is provided at run time variable definition syntax can be used inside the function header code examples hello world program print hello world program to calculate the factorial of a non negative integer text input type a number and its factorial will be printed n int text if n 0 raise valueerror you must enter a non negative integer factorial 1 for i in range 2 n 1 factorial i print factorial libraries python s large standard library 124 is commonly cited as one of its greatest strengths for internet facing applications many standard formats and protocols such as mime and http are supported the language includes modules for creating graphical user interfaces connecting to relational databases generating pseudorandom numbers arithmetic with arbitrary precision decimals 120 manipulating regular expressions and unit testing some parts of the standard library are covered by specifications for example the web server gateway interface wsgi implementation wsgiref follows pep 333 125 but most parts are specified by their code internal documentation and test suites however because most of the standard library is cross platform python code only a few modules must be altered or rewritten for variant implementations as of 13 march 2025 update the python package index pypi the official repository for third party python software contains over 614 339 126 packages development environments see also comparison of integrated development environments python most which python implementations including cpython include a read eval print loop repl this permits the environment to function as a command line interpreter with which users enter statements sequentially and receive results immediately 127 also cpython is bundled with an integrated development environment ide called idle 128 which is oriented toward beginners citation needed by whom other shells including idle and ipython add additional capabilities such as improved auto completion session state retention and syntax highlighting 128 129 standard desktop ides include pycharm spyder and visual studio code 130 there are web browser based ides such as the following environments jupyter notebooks an open source interactive computing platform 131 pythonanywhere a browser based ide and hosting environment and canopy a commercial ide from enthought that emphasizes scientific computing 132 133 implementations see also list of python software python implementations reference implementation cpython is the reference implementation of python this implementation is written in c meeting the c11 standard 134 since version 3 11 older versions use the c89 standard with several select c99 features but third party extensions are not limited to older c versions e g they can be implemented using c11 or c 135 136 cpython compiles python programs into an intermediate bytecode 137 which is then executed by a virtual machine 138 cpython is distributed with a large standard library written in a combination of c and native python cpython is available for many platforms including windows and most modern unix like systems including macos and apple m1 macs since python 3 9 1 using an experimental installer starting with python 3 9 the python installer intentionally fails to install on windows 7 and 8 139 140 windows xp was supported until python 3 5 old python versions unofficially support vms mostly supporting 141 and openvms x86 64 has python 3 10 support 142 143 platform portability was one of python s earliest priorities 144 during development of python 1 and 2 even os 2 and solaris were supported 8 since that time support has been dropped for many platforms all current python versions since 3 7 support only operating systems that feature multithreading by now supporting not nearly as many operating systems dropping many outdated than in the past limitations of the reference 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