Values

  • Value = the "worth" of something

  • Values are fundamental representations of data/information inside a computer program

  • Computer programs operate/manipulate/transform values !

  • Example of values: 

      1               an integer number 
  3.14		  an floating point number
  "Hello"         a text/string with 5 letters
  True            a logical value

     

Data types

  • Every value has a (data) type

  • Examples: 

       Value       Python Data type      
  ==============================
     1            int           the whole numbers
     3.14         float         the real numbers
     "Hello"      string        text
     True         boolean       logical values (True/False)

  • Command to find the type of a value: 

          type(value)  

>>> type(4)
<class 'int'>
>>> type("Hello")
<class 'str'>

Exercise

  • What is the type of the following values: 

      type(1)

  type("1")

  type(3.14)

  type("3.14)

  type(True)

  type("True")

  type('True')

Exercise

  • What is the type of the following values:   (Answers): 

      type(1)                  integer

  type("1")		   string !

  type(3.14)		   float

  type("3.14)		   string !

  type(True)		   boolean

  type("True")		   string !

  type('True')		   string ! (single quote works too)

The special value None in Python

  • The special value denoted by: 

          None

    is used to denote/represent no value

  • The data type of None is:   NoneType 

    >>> type(None)
<class 'NoneType'>

  • Note:

    • None is not the same as the integer 0 !
    • None is not the same as the empty string "" !

Why do we need a type for a value ?

  • Recall that we can only store numbers (= values) inside the computer (memory):

  • The data type provides the context on how to interpret the number (value)

  • Key to understand information:

      • Information   =   data (=value)   +   context (interprete data)

How computer represent (= interpret) integer values

  • Recall:   computer can store integer numbers:

  • How computers represent integer values:

      • Integer values are represented naively (= straightforwardly) using integer numbers inside a computer

How computer represent (= interpret) floating point values

  • A floating point value consists of 2 parts: 

      (1) A  mantissa
  (2) An exponent

  Example:     123.45678   =   0.12345678 × 103  

  Mantissa = 12345678      Exponent = 3

  • How computers represent floating point values:

      • Floating point values are represented using 2 integers

        1. An integer that represents the mantissa
        2. An integer that represents the exponent

    (I.e.: we need to know the type of a value in order to know how we must interpret the integer number(s) !)

How computer represent (= interpret) characters (text)

  • A text is a string of letters/symbols from som alphabet

  • Each letter/symbol of the alphabet is encoded by a unique integer value

  • The universal code used to represent all symbols in the world's lamguages is the Unicode:  

  • Examples: 

     English   Character code    Other    Character code
 ========================    ==========================
   A           65             α       945  (Greek)
   B           66	      א      (1488-Hebrew)
   a	       97	      花      33457 (Chinese)
   b	       98
   0           48
   1	       49

    (One more example that shows that we need to know the type of a value in order to know how we must interpret the integer number(s) !)

How computer represent (= interpret) boolean values

  • There are only 2 boolean values:

      1. True
      2. False

  • How computers represent boolean values: 

     False:       the number 0
 True:        any number other than 0

    (One more example that shows that we need to know the type of a value in order to know how we must interpret the integer number(s) !)