Python Data Types and Expressions

Learning Python syntax on paper is only part of the work. To test commands, investigate mistakes, and see what Python does with an expression, you need to run the interpreter. Interactive mode makes this possible one command at a time: you enter a command, see Python's response immediately, and then continue with another command.

Before starting, Python must be installed on your machine. Open a terminal or command window, then type python and press Enter. The exact way to open a terminal differs by operating system, but the purpose is the same: provide a text-based interface for entering commands.

When the interpreter starts, Python displays a welcome message that includes version information and brief help text. The most important part for your next action is the >>> prompt. It is Python's signal that the interpreter is ready to receive your command.

The prompt is also a status indicator. When >>> is visible, Python is waiting for input. If it is missing or replaced by something else, Python may still be processing the previous command, or something may have gone wrong. The prompt tells you when it is appropriate to enter the next command.

Once >>> appears, enter a simple mathematical expression. The source example uses 2 + 3. After you press Enter, Python evaluates the arithmetic and displays 5 on the next line. A new >>> prompt then appears.

Interactive mode follows a repeating read-evaluate-print cycle. Python reads the command you enter, evaluates it, prints the result, and displays a new >>> prompt. The cycle then waits for your next command. The 2 + 3 interaction is one complete pass through this cycle.

This cycle is what makes interactive mode useful for learning and debugging. Instead of writing a complete script and running everything at once, you can try one command, inspect the immediate result, and then decide what to enter next.