module 2

• Common data types


  • integer
  • float
  • string
  • boolean
• Weak/Strong typing


  Weak typing focuses on convenience, allowing automatic conversion between types. Strong typing focuses on safety, requiring explicit conversion.
• Implicit and explicit conversion

  Implicit conversion is automatic, while explicit conversion is done manually by the programmer.
• Static and dynamic typing

  Static typing requires declaring variable types, dynamic typing determines types based on assigned values.
• Numeric, string and boolean conversions

  • int
  • float
  • str
  • bool
• Selection statements


  • If-then
  • If-then-else
  • Else-if
• Boolean expressions


  Expressions that evaluate to True or False
• Comparison operators


  • <
  • <=
  • >
  • >=
  • ==
  • !=
• Variables allow assigning a name to data stored in memory for later use
• Data types are the "categories" of data, determining how the computer interprets the values
• Most common data types

  • integer
  • float
  • string
  • boolean
• Some languages have additional numeric data types for very large numbers or large fractional parts
• Some languages, like C, do not have a string data type, only a "character" type
• Weak typing


  Languages that focus on convenience by making it easier to mix and automatically convert data types
• Strong typing


  Languages that focus on safety by limiting the ability to mix data types, requiring explicit conversion
• Conversion between data types can fail or result in data loss if it doesn't make sense
• Many languages do implicit (automatic) conversion between compatible data types as needed, known as coercion
• Static typing


  Requires declaring variable types, which must be adhered to
• Dynamic typing


  Determines variable types based on assigned values, no declaration required
• In statically typed languages, trying to assign a value of a different type results in an error or coercion
• In dynamically typed languages, variables can hold values of different types over time
• Input() always returns user input as a string, requiring conversion for arithmetic
• Selection statements allow choosing which code to run based on a condition
• The most common selection statement is if-then, which runs code if a boolean expression is true
• If-then statements can be extended with else and else-if
• Boolean expressions evaluate to true or false, often using comparison operators
• Non-boolean values can be coerced to true or false
• Selection statements


  Choose which code to run based upon the result of a boolean expression - i.e. An expression that results in either True or False
• Comparison operator


  Used to compare values and receive a True or False result
• Function


  Will return (result in) either True or False
• Boolean value


  A non-boolean value can be coerced to either True or False
• Comparison Operators


  • 
    
  • Less than
  • Less than or equal to
  • Greater than
  • Greater than or equal to
  • Equal to
  • Not equal to
• If-Then / Boolean Expression Examples

  • Comparing a numeric variable to a number
  • Using a function in a comparison
  • Using a boolean value returned from a function
  • Using a coerced boolean value
• Logical operators


  Used to make multiple comparisons in a boolean expression
• Logical Operators


  • and
  • or
  • not
• Python uses "and", "or" and "not" for logical operators
• and


  True if both comparisons are true, otherwise false
• or


  True if either (or both) comparison is true, false if they are both false
• not


  Reverse/Flip true and false
• Logical operators are evaluated after evaluating the expressions on either side of them to True/False