How Python Programs are Executed

Lecture 6:- How Python Programs are Executed

Python programs are executed using the Python interpreter, which is a software application that reads and executes Python code. The process of executing a Python program involves several steps:

Source Code: You start by writing the Python program in a text file with a .py extension. This file contains the human-readable Python code that you want to run.
Lexical Analysis: When you run a Python script, the Python interpreter reads the source code character by character. The first step is lexical analysis, where the interpreter breaks down the source code into smaller units called tokens. Tokens include keywords, identifiers, literals, operators, and other language-specific elements.
Parsing: After the lexical analysis, the interpreter parses the tokens to create a data structure called an Abstract Syntax Tree (AST). The AST represents the hierarchical structure of the Python code, making it easier for the interpreter to understand the program's logic.
Compilation (optional): In some cases, Python can compile the AST into bytecode using its built-in compiler. Compiled bytecode is a lower-level representation of the Python program that can be executed more efficiently than the original source code. This step is optional as Python is an interpreted language, but bytecode compilation can improve performance.
Runtime Execution: Once the AST is generated (and optionally compiled to bytecode), the interpreter starts executing the program from the top, line by line. It interprets each line and executes the corresponding operations.
Dynamic Typing: Python is dynamically typed, meaning variable types are determined at runtime. As the interpreter encounters variables, it automatically identifies their types and allocates memory accordingly.
Importing Modules: If your Python program includes import statements to use external modules or libraries, the interpreter will locate, load, and execute those modules as well.
Execution Flow: The interpreter follows the flow of control statements (e.g., if-else, loops) and function calls, executing code based on conditions and user-defined functions.
Output and Errors: During execution, the Python program may produce output (e.g., print statements) or raise errors if something goes wrong. The interpreter handles these outputs and errors as they occur.
Termination: The program continues to execute until it reaches the end of the script or encounters a specific exit condition (e.g., a sys.exit() call). At this point, the Python interpreter terminates, and the program execution is complete.

It's important to note that Python is an interpreted language, meaning it is executed line-by-line at runtime by the interpreter. This differs from compiled languages like C or C++, where the code is transformed into machine code before execution. The dynamic nature of Python allows for flexibility and ease of development, but it may be slightly slower compared to compiled languages. However, Python's ease of use and readability often make it a preferred choice for many applications.