Is Python interpreted or compiled or both

Question

From my understanding   An interpreted language is a high-level language run and executed by an interpreter  a program which converts the high-level language to machine code and then executing  on the go  it processes the program a little at a time   A compiled language is a high-level language whose code is first converted to machine-code by a compiler  a program which converts the high-level language to machine code  and then executed by an executor  another program for running the code    Correct me if my definitions are wrong   Now coming back to Python  I am bit confused about this  Everywhere you learn that Python is an interpreted language  but it s interpreted to some intermediate code  like byte-code or IL  and not to the machine code  So which program then executes the IM code  Please help me understand how a Python script is handled and run

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According to the official Python site  it s interpreted  https   www python org doc essays blurb   Python is an interpreted  object-oriented  high-level programming language          Since there is no compilation step           The Python interpreter and the extensive standard library are available          Instead  when the interpreter discovers an error  it raises an exception  When the program doesn t catch the exception  the interpreter prints a stack trace

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It really depends on the implementation of the language being used  There is a common step in any implementation  though  your code is first compiled  translated  to intermediate code - something between your code and machine  binary  code - called bytecode  stored into  pyc files   Note that this is a one-time step that will not be repeated unless you modify your code  And that bytecode is executed every time you are running the program  How  Well  when we run the program  this bytecode  inside a  pyc file  is passed as input to a Virtual Machine  VM 1 - the runtime engine allowing our programs to be executed - that executes it  Depending on the language implementation  the VM will either interpret the bytecode  in the case of CPython2 implementation  or JIT-compile3 it  in the case of PyPy4 implementation   Notes  1 an emulation of a computer system 2 a bytecode interpreter  the reference implementation of the language  written in C and Python - most widely used 3 compilation that is being done during the execution of a program  at runtime  4 a bytecode JIT compiler  an alternative implementation to CPython  written in RPython  Restricted Python  - often runs faster than CPython

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Python the interpreter  is compiled          Proof   It won t even compile your code if it contains syntax error    Example 1            print  This should print    a   9 0    Output   This should print Traceback  most recent call last     File  p py   line 2  in  lt module gt      a   9 0 ZeroDivisionError  integer division or modulo by zero      Code gets compiled successfully  First line gets executed  print  second line throws ZeroDivisionError  run time error      Example 2          print  This should not print    0            Output        File  p py   line 2      0       SyntaxError  invalid syntax      Conclusion  If your code file contains SyntaxError nothing will execute as compilation fails

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Almost  we can say Python is interpreted language  But we are using some part of one time compilation process in python to convert complete source code into byte-code like java language

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Its a big confusion for the people who started working on python and the answers here are a little difficult to comprehend so i ll make it easier  When we instruct Python to run our script  there are a few steps that Python carries out before our code actually starts crunching away   It is compiled to bytecode  Then it is routed to virtual machine   When we execute a source code  Python compiles it into a byte code  Compilation is a translation step  and the byte code is a low-level platform-independent representation of source code  Note that the Python byte code is not binary machine code  e g   instructions for an Intel chip   Actually  Python translate each statement of the source code into byte code instructions by decomposing them into individual steps  The byte code translation is performed to speed execution  Byte code can be run much more quickly than the original source code statements  It has pyc extension and it will be written if it can write to our machine  So  next time we run the same program  Python will load the  pyc file and skip the compilation step unless it s been changed  Python automatically checks the timestamps of source and byte code files to know when it must recompile  If we resave the source code  byte code is automatically created again the next time the program is run  If Python cannot write the byte code files to our machine  our program still works  The byte code is generated in memory and simply discarded on program exit  But because  pyc files speed startup time  we may want to make sure it has been written for larger programs  Let s summarize what happens behind the scenes  When a Python executes a program  Python reads the  py into memory  and parses it in order to get a bytecode  then goes on to execute  For each module that is imported by the program  Python first checks to see whether there is a precompiled bytecode version  in a  pyo or  pyc  that has a timestamp which corresponds to its  py file  Python uses the bytecode version if any  Otherwise  it parses the module s  py file  saves it into a  pyc file  and uses the bytecode it just created  Byte code files are also one way of shipping Python codes  Python will still run a program if all it can find are pyc files  even if the original  py source files are not there  Python Virtual Machine  PVM  Once our program has been compiled into byte code  it is shipped off for execution to Python Virtual Machine  PVM   The PVM is not a separate program  It need not be installed by itself  Actually  the PVM is just a big loop that iterates through our byte code instruction  one by one  to carry out their operations  The PVM is the runtime engine of Python  It s always present as part of the Python system  It s the component that truly runs our scripts  Technically it s just the last step of what is called the Python interpreter

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First off  interpreted compiled is not a property of the language but a property of the implementation  For most languages  most if not all implementations fall in one category  so one might save a few words saying the language is interpreted compiled too  but it s still an important distinction  both because it aids understanding and because there are quite a few languages with usable implementations of both kinds  mostly in the realm of functional languages  see Haskell and ML   In addition  there are C interpreters and projects that attempt to compile a subset of Python to C or C   code  and subsequently to machine code    Second  compilation is not restricted to ahead-of-time compilation to native machine code  A compiler is  more generally  a program that converts a program in one programming language into a program in another programming language  arguably  you can even have a compiler with the same input and output language if significant transformations are applied   And JIT compilers compile to native machine code at runtime  which can give speed very close to or even better than ahead of time compilation  depending on the benchmark and the quality of the implementations compared    But to stop nitpicking and answer the question you meant to ask  Practically  read  using a somewhat popular and mature implementation   Python is compiled  Not compiled to machine code ahead of time  i e   compiled  by the restricted and wrong  but alas common definition    only  compiled to bytecode  but it s still compilation with at least some of the benefits  For example  the statement a   b c   is compiled to a byte stream which  when  disassembled   looks somewhat like load 0  b   load str  c   get attr  call function 0  store 1  a   This is a simplification  it s actually less readable and a bit more low-level -  you can experiment with the standard library dis module and see what the real deal looks like  Interpreting this is faster than interpreting from a higher-level representation   That bytecode is either interpreted  note that there s a difference  both in theory and in practical performance  between interpreting directly and first compiling to some intermediate representation and interpret that   as with the reference implementation  CPython   or both interpreted and compiled to optimized machine code at runtime  as with PyPy

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If   You know Java      Python code is converted into bytecode like java does  That bytecode is executed again everytime you try to access it    else    Python code is initially traslated into something called bytecode that is quite  close to machine language but not actual machine code so each time we access or run it that bytecode is executed again

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The python code you write is compiled into python bytecode  which creates file with extension  pyc  If compiles  again question is  why not compiled language    Note that this isn t compilation in the traditional sense of the word  Typically  we   d say that compilation is taking a high-level language and converting it to machine code  But it is a compilation of sorts  Compiled in to intermediate code not into machine code  Hope you got it Now    Back to the execution process  your bytecode  present in pyc file  created in compilation step  is then executed by appropriate virtual machines  in our case  the CPython VM  The time-stamp  called as magic number  is used to validate whether  py file is changed or not  depending on that new pyc file is created  If pyc is of current code then it simply skips compilation step

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Yes  it is both compiled and interpreted language  Then why we generally call it as interpreted language   see how it is both- compiled and interpreted   First of all I want to tell that you will like my answer more if you are from the Java world   In the Java the source code first gets converted to the byte code through javac compiler then directed to the JVM responsible for generating the native code for execution purpose   Now I want to show you that we call the Java as compiled language because we can see that it really compiles the source code and gives the  class file nothing but bytecode  through   javac Hello java  -------  produces Hello class file  java Hello -------- Directing bytecode to JVM for execution purpose  The same thing happens with python i e  first the source code gets converted to the bytecode through the compiler then directed to the PVM responsible for generating the native code for execution purpose   Now I want to show you that we usually call the Python as an interpreted language because the compilation happens behind the scene and when we run the python code through    python Hello py -------  directly excutes the code and we can see the output provied that code is syntactically correct    python Hello py it looks like it directly executes but really it first generates the bytecode that is interpreted by the interpreter to produce the native code for the execution purpose   CPython- Takes the responsibility of both compilation and interpretation   Look into the below lines if you need more detail   As I mentioned that CPython compiles the source code but actual compilation happens with the help of cython then interpretation happens with the help of CPython  Now let s talk a little bit about the role of Just-In-Time compiler in Java and Python  In JVM the Java Interpreter exists which interprets the bytecode line by line to get the native machine code for execution purpose but when Java bytecode is executed by an interpreter  the execution will always be slower  So what is the solution  the solution is Just-In-Time compiler which produces the native code which can be executed much more quickly than that could be interpreted  Some JVM vendors use Java Interpreter and some use Just-In-Time compiler  Reference  click here  In python to get around the interpreter to achieve the fast execution use another python implementation PyPy  instead of CPython  click here for other implementation of python including PyPy

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The answer depends on what implementation of python is being used  If you are using lets say CPython  The Standard implementation of python  or Jython  Targeted for integration with java programming language it is first translated into bytecode  and depending on the implementation of python you are using   this bycode is directed to the corresponding virtual machine for interpretation  PVM  Python Virtual Machine  for CPython and JVM  Java Virtual Machine  for Jython   But lets say you are using PyPy which is another standard CPython implementation  It would use a Just-In-Time Compiler

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For newbies  Python automatically compiles your script to compiled code  so called byte code  before running it   Running a script is not considered an import and no  pyc will be created   For example  if you have a script file abc py that imports another module xyz py  when you run abc py  xyz pyc will be created since xyz is imported  but no abc pyc file will be created since abc py isn   t being imported

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The CPU can only understand machine code indeed  For interpreted programs  the ultimate goal of an interpreter is to  interpret  the program code into machine code  However  usually a modern interpreted language does not interpret human code directly because it is too inefficient   The Python interpreter first reads the human code and optimizes it to some intermediate code before interpreting it into machine code  That s why you always need another program to run a Python script  unlike in C   where you can run the compiled executable of your code directly  For example  c  Python27 python exe or  usr bin python

[python] Is Python interpreted, or compiled, or both?

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