Interactive mode vs script mode

Hello students, welcome to Kwickprep. You type fifteen plus ten in Python and see twenty five. You save the same line in a file, run it, and see nothing. Why? Today we will learn the two ways to run Python, interactive mode and script mode, and when to use each.

First, some new words. The interpreter is the program that reads your Python code and runs it. In interactive mode, you type one line, press Enter, and the interpreter answers at once. In script mode, you write many lines in a file first, and then run the whole file together. That file is called a script, and its name ends in dot pie, like bill dot pie.

When you open the Python shell, you see three arrow marks. This is called the prompt, and it means Python is waiting for you. Type fifteen plus ten and press Enter. Python shows twenty five straight away, with no print needed. Now store Surat in a variable called city. Type just city, and Python shows its value, with quotes around it.

There are two easy ways to reach this prompt. Open IDLE, the editor that comes with Python, and its Shell window shows the prompt. Or open a terminal or command prompt and type python, or python three on a Mac. When you are done, type exit with round brackets to leave.

Now script mode. In IDLE, click File, then New File, and type these four lines. Save the file as bill dot pie. Press the F five key, or choose Run Module. Python runs every line from top to bottom. The print function shows the text Canteen bill, and then twenty five.

Here is the trap from the start of the lesson. Echo means Python shows a value on its own, without print. The shell echoes values, but a script does not. Pause and predict. How many times does twenty five appear when this runs as a script? Only once. The line with just bill does nothing in a script, so only print shows the answer.

Let us compare the two modes side by side. Interactive mode runs one line at a time, while script mode runs the whole file. Interactive work is lost when you close the shell, but a script stays saved. The shell shows values on its own, but a script shows them only with print. Interactive mode is best for quick tests, and script mode is for real programs. To fix a mistake in the shell you retype lines, but in a script you edit and simply run again.

Programmers use both modes together. Suppose you forget what division gives in Python. Test it in the shell before writing your program. One slash is normal division, so seven divided by two gives three point five. Two slashes is floor division, which keeps only the whole number part, so we get three. The percent sign is the modulus operator, which gives the remainder, so we get one.

Now that you know the answers, write the real program as a script. Seven students sit two to a bench. Floor division gives the number of full benches, which is three. Modulus gives the students left over, which is one. The file is saved, so you can change seven to forty tomorrow and run it again.

Mistakes behave a little differently in each mode. In the shell, you see the error, and the prompt comes back so you can try again. In a script, a name error stops Python at that line, but the lines above it have already run and printed. A syntax error, like a missing bracket, is caught before the script starts, so not even the first line runs. The message tells you the line number and the error name.

Let us revise what we learned today. Interactive mode shows a prompt and answers each line at once. Script mode runs a saved dot pie file from top to bottom. The shell shows values on its own, but a script needs print. So test small ideas in the shell, and build your real programs as scripts.