CBSE Class 11 Computer Science Introduction To Python Notes

1.1 Introduction:

- General-purpose Object Oriented Programming language.
- High-level language
- Developed in late 1980 by Guido van Rossum at National Research Institute for Mathematics and Computer Science in the Netherlands.
- It is derived from programming languages such as ABC, Modula 3, small talk, Algol-68.
- It is Open Source Scripting language.
- It is Case-sensitive language (Difference between uppercase and lowercase letters).
- One of the official languages at Google.

1.2 Characteristics of Python:

- Interpreted: Python source code is compiled to byte code as a .pyc file, and this byte code can be interpreted by the interpreter.
- Interactive
- Object Oriented Programming Language
- Easy & Simple
- Portable
- Scalable: Provides improved structure for supporting large programs.
- Integrated
- Expressive Language

1.3 Python Interpreter:
Names of some Python interpreters are:

- PyCharm
- Python IDLE
- The Python Bundle
- pyGUI
- Sublime Text etc.
- There are two modes to use the python interpreter:
i. Interactive Mode
ii. Script Mode

i. Interactive Mode: Without passing python script file to the interpreter, directly execute code to Python (Command line).
Example:

>>>6+3
Output: 9

Note: >>> is a command the python interpreter uses to indicate that it is ready. The interactive mode is better when a programmer deals with small pieces of code.
To run a python file on command line:
exec(open(“C:\Python33\python programs\program1.py”).read( ))

Example:
if you have a file name Demo.py , to run the script you have to follow the following steps:

Step-1: Open the text editor i.e. Notepad
Step-2: Write the python code and save the file with .py file extension. (Default directory is C:\Python33/Demo.py)
Step-3: Open IDLE ( Python GUI) python shell
Step-4: Click on file menu and select the open option
Step-5: Select the existing python file
Step-6: Now a window of python file will be opened
Step-7: Click on Run menu and the option Run Module.
Step-8: Output will be displayed on python shell window.