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.