Python Execution Modes

Execution Modes

• There are two ways to use the Python interpreter: Interactive mode and Script mode.
• Interactive mode allows execution of individual statements instantaneously, and is convenient for testing a single line of code for instant execution.
• Script mode allows us to write more than one instruction in a file called a Python source code file that can be executed.

Interactive Mode

• To work in interactive mode, we can simply type a Python statement on the >>> prompt directly.
• As soon as we press enter, the interpreter executes the statement and displays the result(s).
• In interactive mode, we cannot save the statements for future use and have to retype the statements to run them again.

Script Mode

• In script mode, we can write a Python program in a file, save it, and then use the interpreter to execute it.
• Python scripts are saved as files with extension “.py”.
• By default, the Python scripts are saved in the Python installation folder.
• There are two ways to create a script file: create a python file (.py) from IDLE (“File” ➔”New File”), and save it, or create a Python file (.py) using an editor like Notepad++, save it, and then open it directly from IDLE (“File” ➔”Open”).

Installing PyCharm

• PyCharm is one of the best IDEs for Python.
• When you install the Python language on your computer, one of the items that is installed is the Python interpreter.
• The Python interpreter can run Python programs that are saved in files or interactively execute Python statements that are typed at the keyboard.
• Python comes with a program named IDLE that simplifies the process of writing, executing, and testing programs.

Python IDE/IDLE

• Python IDLE (Integrated Development and Learning Environment) is an integrated development environment for Python, which has been bundled with the default implementation of the language.
• IDLE provides comprehensive facilities to computer programmers for software development.
• Most modern IDEs have intelligent code completion.

Installing Python and PyCharm IDE

• To install Python, go to www.python.org and click on “Downloads” link at the top of the page, then click on “Download Python 3.11.2”.
• After installation, the Python interpreter is installed on your computer to run and execute python programs.

Running Python

• The interpreter is also called Python shell.
• A sample screen of Python interpreter (or shell) is shown in the following figure.
• The symbol >>> is the Python prompt, which indicates that the interpreter is ready to take instructions.

Variables in Python

• A variable in Python refers to an object — an item or element that is stored in the memory.
• Value of a variable can be a string (e.g., ‘b’, ‘Global Citizen’), numeric (e.g., 345) or any combination of alphanumeric characters (CD67).
• In Python, we can use an assignment statement to create new variables and assign specific values to them.
• Variable declaration is implicit in Python, means variables are automatically declared and defined when they are assigned a value the first time.
• Variables must always be assigned values before they are used in expressions, otherwise, it will lead to an error in the program.
• Wherever a variable name occurs in an expression, the interpreter replaces it with the value of that particular variable.

Comments in Python

• Comments are used to add a remark or a note in the source code.
• Comments are not executed by the interpreter.
• In Python, a comment starts with # (hash sign).
• Everything following the # till the end of that line is treated as a comment and the interpreter simply ignores it while executing the statement.

Everything is an Object

• Python treats every value or data item whether numeric, string, or other type as an object in the sense that it can be assigned to some variable or can be passed to a function as an argument.