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Relational and Boolean Operators

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

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  1. Relational and Boolean Operators CSIS 1595: Fundamentals of Programming and Problem Solving 1

  2. 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 =)

  3. Relational Operators Example

  4. 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

  5. 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

  6. 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

  7. 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: …

  8. 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

  9. Boolean Expressions • Syntax: conditionalExprbooleanOpconditionalExpr • Examples: • if x >= 1 and x <= 10: … • if a != 0 or b != 0: …

  10. 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

  11. 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): …

  12. 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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