Programming in Python

Programming in Python

In Python, programs can be written in two ways namely Interactive mode and Script mode. The Interactive mode allows us to write codes in Python command prompt (>>>) whereas in script mode programs can be written and stored as separate file with the extension.py and executed. Script mode is used to create and edit python source file.

Interactive mode Programming

In interactive mode Python code can be directly typed and the interpreter displays the result(s) immediately. The interactive mode can also be used as a simple calculator.

(i) Invoking Python IDLE

The following command can be used to invoke Python IDLE from Window OS.

Start → All Programs → Python 3.x → IDLE (Python 3.x)

(Or)

Click python  Icon on the Desktop if available.

Now Python IDLE window appears as shown in the Figure 5.1

The prompt (>>>) indicates that Interpreter is ready to accept instructions. Therefore, the prompt on screen means IDLE is working in interactive mode. Now let us try as a simple calculator by using a simple mathematical expressions.

Example 1:

>>> 5 + 10

15

>>> 5 + 50 *10

505

>>> 5 ** 2

25

Example 2:

>>>print (“Python Programming Language”)

Python Programming Language

>>>x=10

>>>y=20

>>>z=x + y

>>>print (“The Sum”, z)

The Sum = 30

Script mode Programming

Basically, a script is a text file containing the Python statements. Python Scripts are reusable code. Once the script is created, it can be executed again and again without retyping. The Scripts are editable.

(i) Creating Scripts in Python

1. Choose File → New File or press Ctrl + N in Python shell window.

2. An untitled blank script text editor will be displayed on screen as shown in Figure 5.3(a)

3. Type the following code in Script editor

a =100

b = 350

c = a+b

print ("The Sum=", c)

(ii) Saving Python Script

(1) Choose File → Save or Press Ctrl + S

(2) Now, Save As dialog box appears on the screen as shown in the Figure 5.6

(3) In the Save As dialog box, select the location where you want to save your Python code, and type the file name in File Name box. Python files are by default saved with extension.py. Thus, while creating Python scripts using Python Script editor, no need to specify the file extension.

(4) Finally, click Save button to save your Python script.

(iii) Executing Python Script

(1) Choose Run → Run Module or Press F5

(2) If your code has any error, it will be shown in red color in the IDLE window, and Python describes the type of error occurred. To correct the errors, go back to Script editor, make corrections, save the file using Ctrl + S or File → Save and execute it again.

(3) For all error free code, the output will appear in the IDLE window of Python as shown in Figure 5.8