[301] Conditions Based on slides created by Tyler Caraza-Harter - PowerPoint PPT Presentation

[301] Conditions Based on slides created by Tyler Caraza-Harter

Learning Objectives Today Reason about conditions • Conditional execution Chapter 5 of Think Python • Alternate execution (skip “Recursion” sections) • Chained execution • Nested conditions Understand code blocks • Be able to identify the lines of code in the same block Sanity checking • Recognize errors • Sanitize bad data automatically

Today's Outline Review Control Flow Diagrams Basic syntax for “if” Identifying code blocks Demos


 Indentation Example what does it print? print(“A”) 
 print(“B”) 
 def print_letters (): 
 print(“C”) 
 print(“D”) print(“E”) 
 print(“F”) print_letters()


 Indentation Example what does it print? print(“A”) 
 A 
 print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 print(“D”) F 
 C 
 print(“E”) 
 print(“F”) D print_letters()


 Indentation Example what does it print? print(“A”) 
 A 
 print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 indented, so “inside” 
 print_letters function print(“D”) F 
 C 
 print(“E”) 
 print(“F”) D print_letters()


 Indentation Example what does it print? print(“A”) 
 A 
 print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 indented, so “inside” 
 print_letters function print(“D”) F 
 C 
 print(“E”) 
 printed last because 
 print(“F”) print_letters is called last D print_letters()


 Indentation Example what does it print? print(“A”) 
 A 
 print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 indented, so “inside” 
 print_letters function print(“D”) F 
 C 
 print(“E”) 
 print(“F”) D print_letters()


 Indentation Example what does it print? not indented, so print(“A”) 
 A 
 “outside” any function print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 indented, so “inside” 
 print_letters function print(“D”) F 
 C 
 print(“E”) 
 print(“F”) D print_letters()


 Indentation Example what does it print? not indented, so print(“A”) 
 A 
 “outside” any function print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 indented, so “inside” 
 print_letters function print(“D”) F 
 C 
 also not indented, so print(“E”) 
 “outside” any function. print(“F”) D Runs BEFORE 
 print_letters is called print_letters()


 Indentation Example what does it print? not indented, so print(“A”) 
 A 
 “outside” any function print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 indented, so “inside” 
 print_letters function print(“D”) F 
 C 
 also not indented, so print(“E”) 
 “outside” any function. print(“F”) D Runs BEFORE 
 print_letters is called print_letters() We use indenting to tell Python which code is inside or outside 
 of a function (or other things we’ll learn about soon).


 Indentation Example what does it print? not indented, so print(“A”) 
 A 
 “outside” any function print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 indented, so “inside” 
 print_letters function print(“D”) F 
 blank lines are irrelevant C 
 also not indented, so print(“E”) 
 “outside” any function. print(“F”) D Runs BEFORE 
 print_letters is called print_letters() We use indenting to tell Python which code is inside or outside 
 of a function (or other things we’ll learn about soon).


 Indentation Example what does it print? print(“A”) 
 A 
 print(“B”) 
 B 
 def print_letters (): 
 E 
 print(“C”) 
 we’ll often call the lines 
 print(“D”) of code inside something 
 F 
 a “block” of code C 
 print(“E”) 
 print(“F”) D print_letters()

Today's Outline Review Control Flow Diagrams Basic syntax for “if” Identifying code blocks Demos

Control Flow Diagrams x = input(“enter x: ”) x = int(x) x % 2 == 0 False True print(“it’s odd”) print(“it’s even”) print(“thank you”)

Control Flow Diagrams x = input(“enter x: ”) x = int(x) x % 2 == 0 False True Sometimes 
 we do this print(“it’s odd”) print(“it’s even”) print(“thank you”)

Control Flow Diagrams x = input(“enter x: ”) x = int(x) x % 2 == 0 False True Sometimes 
 Other times 
 we do this we do this print(“it’s odd”) print(“it’s even”) print(“thank you”)

Control Flow Diagrams x = input(“enter x: ”) x = int(x) condition x % 2 == 0 False True Sometimes 
 Other times 
 we do this we do this print(“it’s odd”) print(“it’s even”) print(“thank you”)

Control Flow Diagrams x = input(“enter x: ”) x = int(x) boolean expressions are mostly 
 used for deciding what to do next 
 condition (not for printing “True” or “False” 
 is in most of our examples thus far) x % 2 == 0 False True Sometimes 
 Other times 
 we do this we do this print(“it’s odd”) print(“it’s even”) print(“thank you”)

“Paths of Execution” Input/Output: enter x: 7 x = input(“enter x: ”) it’s odd x = int(x) thank you x % 2 == 0 False True print(“it’s odd”) print(“it’s even”) print(“thank you”)

“Paths of Execution” Input/Output: enter x: 8 x = input(“enter x: ”) it’s even x = int(x) thank you x % 2 == 0 False True print(“it’s odd”) print(“it’s even”) print(“thank you”)

Today's Outline Review Control Flow Diagrams Basic syntax for “if” Identifying code blocks Demos

Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x % 2 == 0 False True print(“it’s odd”) print(“it’s even”) print(“thank you”)

Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) x % 2 == 0 False True print(“it’s odd”) print(“it’s even”) print(“thank you”)

Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 False True print(“it’s odd”) print(“it’s even”) print(“thank you”)

Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 False True print(“it’s odd”) print(“it’s even”) boolean expression print(“thank you”)

Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 print(“it’s even”) False True print(“it’s odd”) print(“it’s even”) print(“thank you”)


 Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 print(“it’s even”) else: False True print(“it’s odd”) 
 print(“it’s odd”) print(“it’s even”) print(“thank you”)


 Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 print(“it’s even”) else: False True print(“it’s odd”) 
 print(“thank you”) print(“it’s odd”) print(“it’s even”) print(“thank you”)


 Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 print(“it’s even”) else: False True print(“it’s odd”) 
 print(“thank you”) print(“it’s odd”) print(“it’s even”) print(“thank you”)


 Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 print(“it’s even”) else: False True print(“it’s odd”) print(“good!”) 
 print(“it’s odd”) print(“it’s even”) print(“good!”) print(“thank you”) print(“thank you”)


 Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 print(“it’s even”) 
 print(“we wanted odd”) False True else: print(“it’s odd”) print(“it’s odd”) print(“it’s even”) 
 print(“good!”) 
 print(“good!”) print(“we wanted odd”) print(“thank you”) print(“thank you”)


 Writing conditions in Python Code: x = input(“enter x: ”) x = int(x) x = input(“enter x: ”) x = int(x) if x % 2 == 0: x % 2 == 0 print(“it’s even”) 
 print(“we wanted odd”) False True else: print(“it’s odd”) print(“it’s odd”) print(“it’s even”) 
 print(“good!”) 
 print(“good!”) print(“we wanted odd”) print(“thank you”) print(“all done”) print(“thank you”) print(“all done”)

Today's Outline Review Control Flow Diagrams Basic syntax for “if” Identifying code blocks Demos