If Python is interpreted what are pyc files

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I ve been given to understand that Python is an interpreted language     However  when I look at my Python source code I see  pyc files  which Windows identifies as  Compiled Python Files       Where do these come in

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Python  at least the most common implementation of it  follows a pattern of compiling the original source to byte codes  then interpreting the byte codes on a virtual machine  This means  again  the most common implementation  is neither a pure interpreter nor a pure compiler   The other side of this is  however  that the compilation process is mostly hidden -- the  pyc files are basically treated like a cache  they speed things up  but you normally don t have to be aware of them at all  It automatically invalidates and re-loads them  re-compiles the source code  when necessary based on file time date stamps   About the only time I ve seen a problem with this was when a compiled bytecode file somehow got a timestamp well into the future  which meant it always looked newer than the source file  Since it looked newer  the source file was never recompiled  so no matter what changes you made  they were ignored

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I ve been given to understand that   Python is an interpreted language      This popular meme is incorrect  or  rather  constructed upon a misunderstanding of  natural  language levels  a similar mistake would be to say  the Bible is a hardcover book    Let me explain that simile      The Bible  is  a book  in the sense of being a class of  actual  physical objects identified as  books  the books identified as  copies of the Bible  are supposed to have something fundamental in common  the contents  although even those can be in different languages  with different acceptable translations  levels of footnotes and other annotations  -- however  those books are perfectly well allowed to differ in a myriad of aspects that are not considered fundamental -- kind of binding  color of binding  font s  used in the printing  illustrations if any  wide writable margins or not  numbers and kinds of builtin bookmarks  and so on  and so forth   It s quite possible that a typical printing of the Bible would indeed be in hardcover binding -- after all  it s a book that s typically meant to be read over and over  bookmarked at several places  thumbed through looking for given chapter-and-verse pointers  etc  etc  and a good hardcover binding can make a given copy last longer under such use   However  these are mundane  practical  issues that cannot be used to determine whether a given actual book object is a copy of the Bible or not  paperback printings are perfectly possible   Similarly  Python is  a language  in the sense of defining a class of language implementations which must all be similar in some fundamental respects  syntax  most semantics except those parts of those where they re explicitly allowed to differ  but are fully allowed to differ in just about every  implementation  detail -- including how they deal with the source files they re given  whether they compile the sources to some lower level forms  and  if so  which form -- and whether they save such compiled forms  to disk or elsewhere   how they execute said forms  and so forth   The classical implementation  CPython  is often called just  Python  for short -- but it s just one of several production-quality implementations  side by side with Microsoft s IronPython  which compiles to CLR codes  i e     NET    Jython  which compiles to JVM codes   PyPy  which is written in Python itself and can compile to a huge variety of  back-end  forms including  just-in-time  generated machine language    They re all Python     implementations of the Python language   just like many superficially different book objects can all be Bibles     copies of The Bible     If you re interested in CPython specifically  it compiles the source files into a Python-specific lower-level form  known as  bytecode    does so automatically when needed  when there is no bytecode file corresponding to a source file  or the bytecode file is older than the source or compiled by a different Python version   usually saves the bytecode files to disk  to avoid recompiling them in the future    OTOH IronPython will typically compile to CLR codes  saving them to disk or not  depending  and Jython to JVM codes  saving them to disk or not -- it will use the  class extension if it does save them    These lower level forms are then executed by appropriate  virtual machines  also known as  interpreters  -- the CPython VM  the  Net runtime  the Java VM  aka JVM   as appropriate   So  in this sense  what do typical implementations do   Python is an  interpreted language  if and only if C  and Java are  all of them have a typical implementation strategy of producing bytecode first  then executing it via a VM interpreter   More likely the focus is on how  heavy   slow  and high-ceremony the compilation process is   CPython is designed to compile as fast as possible  as lightweight as possible  with as little ceremony as feasible -- the compiler does very little error checking and optimization  so it can run fast and in small amounts of memory  which in turns lets it be run automatically and transparently whenever needed  without the user even needing to be aware that there is a compilation going on  most of the time   Java and C  typically accept more work during compilation  and therefore don t perform automatic compilation  in order to check errors more thoroughly and perform more optimizations   It s a continuum of gray scales  not a black or white situation  and it would be utterly arbitrary to put a threshold at some given level and say that only above that level you call it  compilation  -

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There is no such thing as an interpreted language  Whether an interpreter or a compiler is used is purely a trait of the implementation and has absolutely nothing whatsoever to do with the language   Every language can be implemented by either an interpreter or a compiler  The vast majority of languages have at least one implementation of each type   For example  there are interpreters for C and C   and there are compilers for JavaScript  PHP  Perl  Python and Ruby   Besides  the majority of modern language implementations actually combine both an interpreter and a compiler  or even multiple compilers    A language is just a set of abstract mathematical rules  An interpreter is one of several concrete implementation strategies for a language  Those two live on completely different abstraction levels  If English were a typed language  the term  interpreted language  would be a type error  The statement  Python is an interpreted language  is not just false  because being false would imply that the statement even makes sense  even if it is wrong   it just plain doesn t make sense  because a language can never be defined as  interpreted    In particular  if you look at the currently existing Python implementations  these are the implementation strategies they are using    IronPython  compiles to DLR trees which the DLR then compiles to CIL bytecode  What happens to the CIL bytecode depends upon which CLI VES you are running on  but Microsoft  NET  GNU Portable NET and Novell Mono will eventually compile it to native machine code  Jython  interprets Python sourcecode until it identifies the hot code paths  which it then compiles to JVML bytecode  What happens to the JVML bytecode depends upon which JVM you are running on  Maxine will directly compile it to un-optimized native code until it identifies the hot code paths  which it then recompiles to optimized native code  HotSpot will first interpret the JVML bytecode and then eventually compile the hot code paths to optimized machine code  PyPy  compiles to PyPy bytecode  which then gets interpreted by the PyPy VM until it identifies the hot code paths which it then compiles into native code  JVML bytecode or CIL bytecode depending on which platform you are running on  CPython  compiles to CPython bytecode which it then interprets  Stackless Python  compiles to CPython bytecode which it then interprets  Unladen Swallow  compiles to CPython bytecode which it then interprets until it identifies the hot code paths which it then compiles to LLVM IR which the LLVM compiler then compiles to native machine code  Cython  compiles Python code to portable C code  which is then compiled with a standard C compiler Nuitka  compiles Python code to machine-dependent C   code  which is then compiled with a standard C compiler   You might notice that every single one of the implementations in that list  plus some others I didn t mention  like tinypy  Shedskin or Psyco  has a compiler  In fact  as far as I know  there is currently no Python implementation which is purely interpreted  there is no such implementation planned and there never has been such an implementation   Not only does the term  interpreted language  not make sense  even if you interpret it as meaning  language with interpreted implementation   it is clearly not true  Whoever told you that  obviously doesn t know what he is talking about   In particular  the  pyc files you are seeing are cached bytecode files produced by CPython  Stackless Python or Unladen Swallow

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They contain byte code  which is what the Python interpreter compiles the source to  This code is then executed by Python s virtual machine    Python s documentation explains the definition like this      Python is an interpreted language  as   opposed to a compiled one  though the   distinction can be blurry because of   the presence of the bytecode compiler    This means that source files can be   run directly without explicitly   creating an executable which is then   run

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Machines don t understand English or any other languages  they understand only byte code  which they have to be compiled  e g   C C    Java  or interpreted  e g   Ruby  Python   the  pyc is a cached version of the byte code  https   www geeksforgeeks org difference-between-compiled-and-interpreted-language  Here is a quick read on what is the difference between compiled language vs interpreted language  TLDR is interpreted language does not require you to compile all the code before run time and thus most of the time they are not strict on typing etc

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To speed up loading modules  Python caches the compiled content of modules in  pyc   CPython compiles its source code into  byte code   and for performance reasons  it caches this byte code on the file system whenever the source file has changes  This makes loading of Python modules much faster because the compilation phase can be bypassed  When your source file is foo py   CPython caches the byte code in a foo pyc file right next to the source   In python3  Python s import machinery is extended to write and search for byte code cache files in a single directory inside every Python package directory  This directory will be called   pycache      Here is a flow chart describing how modules are loaded     For more information   ref PEP3147 ref    Compiled    Python files

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tldr  it s a converted code form the source code  which the python VM interprets for execution  Bottom-up understanding  the final stage of any program is to run execute the program s instructions on the hardware machine  So here are the stages preceding execution   Executing running on CPU  Converting bytcode to machine code   Machine code is the final stage of conversion   Instructions to be executed on CPU are given in machine code  Machine code can be executed directly by CPU     Converting Bytecode to machine code   Bytecode is a medium stage  It could be skipped for efficiency  but sacrificing portability    Converting Source code to bytcode   Source code is a human readable code  This is what is used when working on IDEs  code editors  such as Pycharm     Now the actual plot  There are two approaches when carrying any of these stages  convert  or execute  a code all at once  aka compile  and convert  or execute  the code line by line  aka interpret    For example  we could compile a source code to bytcoe  compile bytecode to machine code  interpret machine code for execution   Some implementations of languages skip stage 3 for efficiency  i e  compile source code into machine code and then interpret machine code for execution   Some implementations skip all middle steps and interpret the source code directly for execution   Modern languages often involve both compiling an interpreting   JAVA for example  compile source code to bytcode  that is how JAVA source is stored  as a bytcode   compile bytcode to machine code  using JVM   and interpret machine code for execution   Thus JVM is implemented differently for different OSs  but the same JAVA source code could be executed on different OS that have JVM installed    Python for example  compile source code to bytcode  usually found as  pyc files accompanying the  py source codes   compile bytocde to machine code  done by a virtual machine such as PVM and the result is an executable file   interpret the machine code executable for execution   When we can say that a language is interpreted or compiled   The answer is by looking into the approach used in execution  If it executes the machine code all at once     compile   then it s a compiled language  On the other hand  if it executes the machine code line-by-line    interpret  then it s an interpreted language    Therefore  JAVA and Python are interpreted languages   A confusion might occur because of the third stage  that s converting bytcode to machine code  Often this is done using a software called a virtual machine  The confusion occurs because a virtual machine acts like a machine  but it s actually not  Virtual machines are introduced for portability  having a VM on any REAL machine will allow us to execute the same source code  The approach used in most VMs  that s the third stage  is compiling  thus some people would say it s a compiled language  For the importance of VMs  we often say that such languages are both compiled and interpreted

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THIS IS FOR BEGINNERS   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   If you need to create a  pyc file for a module that is not imported  you can use the py compile and compileall modules   The py compile module can manually compile any module  One way is to use the py compile compile function in that module interactively    gt  gt  gt  import py compile  gt  gt  gt  py compile compile  abc py     This will write the  pyc to the same location as abc py  you can override that with the optional parameter cfile    You can also automatically compile all files in a directory or directories using the compileall module   python -m compileall   If the directory name  the current directory in this example  is omitted  the module compiles everything found on sys path

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These are created by the Python interpreter when a  py file is imported  and they contain the  compiled bytecode  of the imported module program  the idea being that the  translation  from source code to bytecode  which only needs to be done once  can be skipped on subsequent imports if the  pyc is newer than the corresponding  py file  thus speeding startup a little  But it s still interpreted

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Python s   py file is just a text file in which you write some lines of code  When you try to execute this file using say  python filename py   This command invokes Python Virtual Machine  Python Virtual Machine has 2 components   compiler  and  interpreter   Interpreter cannot directly read the text in   py file  so this text is first converted into a byte code which is targeted to the PVM  not hardware but PVM   PVM executes this byte code    pyc file is also generated  as part of running it which performs your import operation on file in shell or in some other file   If this   pyc file is already generated then every next time you run execute your   py file  system directly loads your   pyc file which won t need any compilation This will save you some machine cycles of processor    Once the   pyc file is generated  there is no need of   py file  unless you edit it

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Python code goes through 2 stages  First step compiles the code into  pyc files which is actually a bytecode  Then this  pyc file bytecode  is interpreted using CPython interpreter  Please refer to this link  Here process of code compilation and execution is explained in easy terms

[python] If Python is interpreted, what are .pyc files?

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