CLASS 11 CS CHAPTER 2

 

CLASS -11  COMPUTER SCIENCE

          CHAPTER-2 PYTHON FUNDAMENTALS

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NOTES FOR COMPLETE UNDERSTANDING -

•  Program, is a group of instructions that controls processing.

•  Or we can say , base for processing is ‘the Program’.

• Elements of processing i.e.– character sets , token, statements, input , expressions .

• Character Set - is a group of letters or signs which are specific to a language.

•  Character set contains alphabets , signs, numbers , symbols . 

1. Letters: A-Z, a-z   
2. Digits: 0-9   
3. Special Symbols: _, +, -, *, /, (, ), {, } . . . etc.     
4. Spaces: blank space, carriage return, newline, form feed , tab ,etc.     
5. It can process all characters of ASCII & UNICODE. 

• Token-
• It is the smallest unit of any programming language and also known as Lexical Unit. 

• Various types of token are-

1. Keywords 
2. Identifiers
3. Literals 
4. Operators 
5. Punctuators

• Keywords are those which provides a special meaning to interpreter and are reserved for specific functioning in coding .

• Keywords can't be used as an identifier , variable name or for any other purpose. 

• Available keywords in Python are -

1. False ,
2. assert,
3. del , 
4. for , 
5. in ,
6. or ,
7. while ,
8. break ,
9. elif , 
10. from ,
11. is ,
12. pass ,
13. with ,
14. True ,
15. else ,
16. global ,
17. lambda ,
18. raise ,
19. yield ,
20. and ,
21. except ,
22. if ,
23. nonlocal ,
24. as ,
25. import ,
26. not ,
27. try, 
28. class ,
29. def ,
30. finally ,
31. is ,
32. return ,
33. None ,
34. continue .

• Identifiers - Identifiers can be considered as building blocks for a program as they are used to locate names to different parts of a program like : variables , objects , class , etc.

• It can be a mixtures of letters & numbers.

•  It must begin with an alphabet or an underscore( _ ). 

• Subsequent letters may be numbers(0-9). 

• Python is case sensitive i.e. the uppercase letters are different from that of  lowercase letters (T and t are different for interpreter).

• Length of an Identifier is unlimited.

• Keywords can't allowed to be used as an identifier.

• Space and special symbols should not be there in an identifier name excluding underscore( _ ) sign.

• Literals are often called Constant Values.

• Python permits following types of literals -                                                                       – String literals - “Pankaj” ,  – Numeric literals – 10, 13.5, 3+5i , – Boolean literals – True or False , – Special Literal None , -Literal collections

• String Literal is a sequence of  combination of letters, numbers and special symbols , enclosed within single , double or triple quotes .
• In python, string is of 2 types-    – Single line string :Text = “Hello World” or Text = ‘Hello World’      – Multi line string :Text = ‘hello\n world’ or Text = ‘’’hello  word ’’  

• Numeric values can be of 3 variants -                                                                                                  
• int (signed integers)

1. Decimal Integer Literals – 11, 137, 2770 etc. 
2. Octal Integer Literals - 0o17, 0o217 etc. 
3. Hexadecimal Integer Literals – 0x15, 0x2A3, 0xABC etc.                                                                                                                                   

• float ( floating point real value) 

1. Fractional Form – 2.07 , 17.555  -13.5,   -0.00015 etc. 
2. Exponent Form - -1.7E+8, .25E-4 etc.                                                                            

• Complex (complex numbers) : 3+5i etc.

• Boolean Literals 
• It can have either of only two values – True or False 

• Special Literals
• Special literal is None, which means nothing (no value): X = None

• Operators
• An Operator can be considered as a representation of some action that has to be applied on  identifier (s)/ operand (s).

•  Concluding that an operator requires operand (s) to compute upon. example : c = a + b Here, a, b, c are operands and operators are = and + which are performing differently

• Types of Operator-   Python supports following types of operators.

• Unary operators:
• Unary plus (+) 
• Unary Minus (-)  
• Binary Operator 
• Arithmetic operator (+, -, *, /, %, **, //) 
• Relational Operator(<, >, <=, >=, ==, != ) 
• Logical Operator (and, or) 
• Assigment Operator (=, /=, +=, -=, *=, %=, **=, //=) 
• Bitwise Operator (& bitwise and, ^ bitwise xor, | bitwise or) 
• Shift operator (<< shift left, >> shift right) 
• Identity Operator (is, is not) 
• Membership Operator (in, not in)
• Punctuators 

•  Punctuators are used to build program & to make balance between instructions and statements .They have their own style of syntactic and semantic recognition. 

•  Python has following Punctuators - ‘ , ” , #, \, (, ), [, ], {, }, @. ,, :, .. `, =

• As we have seen in previous slides, a program contains following components-      – Expressions like a+b, a>b etc.                                                                                    – Statements like a=10, c=a+b etc.                                                                                  – Comments, lines starting with #.                                                                                  – Function, block starting with def keyword                                                                – Blocks and indentation like if and else blocks   

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