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Relational and Boolean Operators. CSIS 1595: Fundamentals of Programming and P roblem Solving 1. Relational Operators. Conditional expressions of form operand1 relationalOperator operand2 Comparing operand1 and operand2 in some way Python relational operators: > greater than

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relational and boolean operators

Relational and Boolean Operators

CSIS 1595: Fundamentals of Programming and Problem Solving 1

relational operators
Relational Operators
  • Conditional expressions of form operand1 relationalOperator operand2
    • Comparingoperand1 and operand2 in some way
  • Python relational operators:

> greater than

< less than

<= less than or equal to

>= greater than or equal to

!= is not equal to

== is equal to

(not same as =)

relational and arithmetic operators
Relational and Arithmetic Operators
  • Can combine in same conditionx = 3y = 7if x * 2 < y + 1: …
  • Precedence: Arithmetic operators done first
    • Evaluate expressions on either side of relational operator to get 2 values
    • Evaluate relational operator in term of those 2 values to get either True or False
relational operators and types
Relational Operators and Types
  • Some operators only make sense for certain types
    • Numbers: > < >= <= == !=
      • Be careful with floats and ==
    • Strings: == !=
      • password = input(“Enter password:”)if password == “xyzzy”: …
        • Can do > < >= <= but get strange results
  • Can only compare similar types

“Fred” > 2  error

equality and float type
Equality and Float Type
  • == checks whether operands are same number
    • Can be problem with floats due to lack of precision

x = 5 * 2/3y = 2/3 * 5if x == y: …  False

equality and float type1
Equality and Float Type
  • Goal: determine whether x and y are “close enough”
    • Within some “margin of error” of each other
  • Method:
    • Compute differencebetween the values
    • Take absolute value
      • Difference may be positive or negative
      • Have built-in abs function
    • Compare with “margin of error” using < instead of ==

x = 5 * 2/3y = 2/3 * 5if abs(x – y) < 0.000001: …

boolean logic
Boolean Logic
  • Some problems involve multiple conditions
    • “x must be between 1 and 10”
    • “either a or b must not be 0”
  • Can create using and, or, other boolean operators
    • x must be greater than or equal to 1 and less than or equal to 10
    • a must not be 0 orb must not be 0
boolean expressions
Boolean Expressions
  • Syntax: conditionalExprbooleanOpconditionalExpr
  • Examples:
    • if x >= 1 and x <= 10: …
    • if a != 0 or b != 0: …
boolean operators
Boolean Operators
  • and: true if both operands are true
    • true and true  true
    • true and false false
    • falseand true false
    • falseand false  false
  • or: true if eitheroperands are true
    • true and true  true
    • true and false  true
    • false and true  true
    • false and false  false
not operator
not Operator
  • not: Reversesboolean value of unary operand
    • Syntax: not conditionalExpr
      • not true false
      • not false  true
    • Example: if not x > 0: …
  • Can often just use “opposite” relational operator
    • if x <= 0: …
  • Commonly used to reverse value of booleanfunction
    • if not math.isfinite(x): …
precedence and boolean operators
Precedence and Boolean Operators
  • Precedence:
    • Evaluate arithmetic expressions in conditional expressions
    • Evaluate conditional expressions to True or False
    • Evaluate boolean operators using those values
      • notevaluated first
      • andevaluated next
      • orevaluated last
    • Can always use () if not sure!
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