Conditionals

• if
• if-else
  • max_value
• if-elsif-else
  • too hot / too cold / just right
• if-elsif-elsif-elsif-else
  • Letter grades
• Indentation matters
  • Spaces different than tabs
• = vs ==
• Operator chaining a < b C
  • somewhat unique to Python
• and / or / not
  • != as shortcut for not x == y
• implicit vs explicit ranges
  • i.e., choosing order of if statements carefully
  • Look at letter grades again.
• chain of if vs. else-if
• nested if
  • Compute bonus for different structures
    • Structure A: 10% for sales over 10,000
    • Structure B: $100 if sales is a multiple of 5.
• integers and floats can be compared. (One is coerced)
• strings can be compared using ==, <, <=, etc.
• can’t directly compare strings and integers
• Avoid comparing float using ==
  • Why?
• is vs ==
• watch for if x = 9: (instead of ==)

  • Example

    def print_discount(has_discount: bool):
      if (has_discount = True):
          print('You have a discount!')
      else 
          print(f"No discount.  (Your status {has_discount})")
          
    print_discount(False)
    

  • Actually, this is a syntax error. Need to use :=.
  • The requirement of the : is to avoid this common mistake.
• Order of operations
  • precedence: not, and, or
  • not x or y is evaluated as (not x) or y.
  • x == 5 or y == 10 and z != 10 is evaluated as (x == 5) or ((y == 10) and (z != 10)) because and has precedence over or.
  • When in doubt, just use parentheses.

• conditional/ ternary operator

  x = 18
  parity = 'even' if x %2 == 0 else 'odd'
  

• Expression trees