Tool Chain of Python Application

  • Python is an object oriented programming language like Java.
  • Python is called an interpreted language.
  • Python uses code modules that are interchangeable instead of a single long list of instructions that was standard for functional programming languages.
  • The standard implementation of python is called “cpython”.
  • It is the default and widely used implementation of the Python.
  • Python doesn’t convert its code into machine code, something that hardware can understand.
  • It actually converts it into something called byte code.
  • So within python, compilation happens, but it’s just not into a machine language.
  • It is into byte code and this byte code can’t be understood by CPU.
  • So we need actually an interpreter called the python virtual machine.
  • The python virtual machine executes the byte codes.

When we instruct Python to run our script, there are a few steps that Python carries out before our code actually starts crunching away:

1. It is compiled to bytecode.

2. Then it is routed to virtual machine.

Python Compiler :-

  • 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 re save 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.
  • 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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