Python vs Cpython

Question

What s all this fuss about Python and CPython  Jython IronPython   I don t get it   python org mentions that CPython is      The  traditional  implementation of Python  nicknamed CPython    yet another Stack Overflow question mentions that      CPython is the default byte-code interpreter of Python  which is written in C    Honestly I don t get what both of those explanations practically mean but what I thought was that  if I use CPython does that mean when I run a sample python code  it compiles it to C language and then executes it as if it were C code  So what exactly is CPython and how does it differ when compared with python and should I probably use CPython over Python and if so what are its advantages

User · Answer

implementation means what language was used to implement Python and not how python Code would be implemented  The advantage of using CPython is the availability of C Run-time as well as easy integration with C C      So CPython was originally implemented using C  There were other forks to the original implementation which enabled Python to lever-edge Java  JYthon  or  NET Runtime  IronPython    Based on which Implementation you use  library availability might vary  for example Ctypes is not available in Jython  so any library which uses ctypes would not work in Jython  Similarly  if you want to use a Java Class  you cannot directly do so from CPython  You either need a glue  JEPP  or need to use Jython  The Java Implementation of Python

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This article thoroughly explains the difference between different implementations of Python  Like the article puts it       The first thing to realize is that    Python    is an interface  There   s a   specification of what Python should do and how it should behave  as   with any interface   And there are multiple implementations  as with   any interface        The second thing to realize is that    interpreted    and    compiled    are   properties of an implementation  not an interface

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Even I had the same problem understanding how are CPython  JPython  IronPython  PyPy are different from each other   So  I am willing to clear three things before I begin to explain    Python  It is a language  it only states describes how to convey express yourself to the interpreter  the program which accepts your python code   Implementation  It is all about how the interpreter was written  specifically  in what language and what it ends up doing  Bytecode  It is the code that is processed by a program  usually referred to as a virtual machine  rather than by the  real  computer machine  the hardware processor       CPython is the implementation  which was   written in C language  It ends up producing bytecode  stack-machine   based instruction set  which is Python specific and then executes it    The reason to convert Python code to a bytecode is because it s easier to   implement an interpreter if it looks like machine instructions  But    it isn t necessary to produce some bytecode prior to execution of the   Python code  but CPython does produce     If you want to look at CPython s bytecode then you can  Here s how you can    gt  gt  gt  def f x  y                    line 1        print  Hello               line 2        if x                       line 3           y    x                  line 4        print x  y                 line 5        return x y                 line 6                                   line 7  gt  gt  gt  import dis                    line 8  gt  gt  gt  dis dis f                     line 9   2           0 LOAD GLOBAL              0  print                2 LOAD CONST               1   Hello                 4 CALL FUNCTION            1               6 POP TOP    3           8 LOAD FAST                0  x               10 POP JUMP IF FALSE       20    4          12 LOAD FAST                1  y               14 LOAD FAST                0  x               16 INPLACE ADD              18 STORE FAST               1  y     5      gt  gt    20 LOAD GLOBAL              0  print               22 LOAD FAST                0  x               24 LOAD FAST                1  y               26 CALL FUNCTION            2              28 POP TOP    6          30 LOAD FAST                0  x               32 LOAD FAST                1  y               34 BINARY ADD 36 RETURN VALUE   Now  let s have a look at the above code  Lines 1 to 6 are a function definition  In line 8  we import the  dis  module which can be used to view the intermediate Python bytecode  or you can say  disassembler for Python bytecode  that is generated by CPython  interpreter    NOTE  I got the link to this code from  python IRC channel  https   gist github com nedbat e89fa710db0edfb9057dc8d18d979f9c  And then  there is Jython  which is written in Java and ends up producing Java byte code  The Java byte code runs on Java Runtime Environment  which is an implementation of Java Virtual Machine  JVM   If this is confusing then I suspect that you have no clue how Java works  In layman terms  Java  the language  not the compiler  code is taken by the Java compiler and outputs a file  which is Java byte code  that can be run only using a JRE  This is done so that  once the Java code is compiled then it can be ported to other machines in Java byte code format  which can be only run by JRE  If this is still confusing then you may want to have a look at this web page   Here  you may ask if the CPython s bytecode is portable like Jython  I suspect not  The bytecode produced in CPython implementation was specific to that interpreter for making it easy for further execution of code  I also suspect that  such intermediate bytecode production  just for the ease the of processing is done in many other interpreters     So  in Jython  when you compile your Python code  you end up with Java byte code  which can be run on a JVM   Similarly  IronPython  written in C  language  compiles down your Python code to Common Language Runtime  CLR   which is a similar technology as compared to JVM  developed by Microsoft

User · Answer

The original  and standard  implementation of Python is usually called CPython when you want to contrast it with the other options  and just plain    Python    otherwise   This name comes from the fact that it is coded in portable ANSI C language code  This is the Python that you fetch from http   www python org  get with the ActivePython and Enthought distributions  and have automatically on most Linux and Mac OS X machines  If you   ve found a preinstalled version of Python on your machine  it   s probably CPython  unless your company or organization is using Python in more specialized ways      Unless you want to script Java or  NET applications with Python or find the benefits   of Stackless or PyPy compelling  you probably want to use the standard CPython system    Because it is the reference implementation of the language  it tends to run the   fastest  be the most complete  and be more up-to-date and robust than the alternative   systems

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You should know that CPython doesn t really support multithreading  it does  but not optimal  because of the Global Interpreter Lock  It also has no Optimisation mechanisms for recursion  and has many other limitations that other implementations and libraries try to fill  You should take a look at this page on the python wiki  Look at the code snippets on this page  it ll give you a good idea of what an interpreter is

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A programming language implementation is a system for executing computer programs   There are two general approaches to programming language implementation    Interpretation  An interpreter takes as input a program in some language  and performs the actions written in that language on some machine  Compilation  A compiler takes as input a program in some language  and translates that program into some other language  which may serve as input to another interpreter or another compiler    Python is an interpreted high-level programming language created by Guido van Rossum in 1991    CPython is reference version of the Python computing language  which is written in C created by Guido van Rossum too   Other list of Python Implementations  Source

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You need to distinguish between a language and an implementation  Python is a language    According to Wikipedia   A programming language is a notation for writing programs  which are specifications of a computation or algorithm   This means that it s simply the rules and syntax for writing code  Separately we have a programming language implementation which in most cases  is the actual interpreter or compiler    Python is a language  CPython is the implementation of Python in C  Jython is the implementation in Java  and so on    To sum up  You are already using CPython  if you downloaded from here

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So what is CPython  CPython is the original Python implementation  It is the implementation you download from Python org  People call it CPython to distinguish it from other  later  Python implementations  and to distinguish the implementation of the language engine from the Python programming language itself  The latter part is where your confusion comes from  you need to keep Python-the-language separate from whatever runs the Python code  CPython happens to be implemented in C  That is just an implementation detail  really  CPython compiles your Python code into bytecode  transparently  and interprets that bytecode in a evaluation loop  CPython is also the first to implement new features  Python-the-language development uses CPython as the base  other implementations follow  What about Jython  etc   Jython  IronPython and PyPy are the current  quot other quot  implementations of the Python programming language  these are implemented in Java  C  and RPython  a subset of Python   respectively  Jython compiles your Python code to Java bytecode  so your Python code can run on the JVM  IronPython lets you run Python on the Microsoft CLR  And PyPy  being implemented in  a subset of  Python  lets you run Python code faster than CPython  which rightly should blow your mind   -  Actually compiling to C So CPython does not translate your Python code to C by itself  Instead  it runs an interpreter loop  There is a project that does translate Python-ish code to C  and that is called Cython  Cython adds a few extensions to the Python language  and lets you compile your code to C extensions  code that plugs into the CPython interpreter

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Python is a language  a set of rules that can be used to write programs  There are several implementaions of this language    No matter what implementation you take  they do pretty much the same thing  take the text of your program and interpret it  executing its instructions  None of them compile your code into C or any other language   CPython is the original implementation  written in C   The  C  part in  CPython  refers to the language that was used to write Python interpreter itself    Jython is the same language  Python   but implemented using Java    IronPython interpreter was written in C    There s also PyPy - a Python interpreter written in Python  Make your pick

[python] Python vs Cpython

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