Python / Making decisions

Logical operators: and, or

Join two conditions into one with and when both must be true, and with or when one is enough. Baccalaureate

Sometimes one condition is not enough. For example, a restaurant gives a discount if 2 or more people come and they have 3000 points or more. You need to check both in a single if.

OperatorMeaningTrue when
A and Bandboth A and B are true
A or Borat least one of A, B is true

and: both conditions

With and the code runs only if every condition holds. If one fails, the whole thing is False:

Python 
people = 3
points = 2500
if people >= 2 and points >= 3000:
    print("20% off")
else:
    print("No 20% discount")
Console
No 20% discount

or: one is enough

With or it is enough for one condition to hold. In the same example, the number of people alone is enough:

Python 
people = 3
points = 2500
if people >= 2 or points >= 3000:
    print("10% off")
Console
10% off

or is handy for checking values outside a range, like a cheaper ticket for children up to 12 or seniors from 65:

Python 
age = 70
if age <= 12 or age >= 65:
    print("30% off")
else:
    print("Full price")
Console
30% off

and is handy for checking a value inside a range, like a mark between 50 and 100:

Python 
mark = 75
if mark >= 50 and mark <= 100:
    print("Passed")
Console
Passed
Write a full condition on both sides of and/or: age <= 12 or age >= 65 is right; age <= 12 or >= 65 is a syntax error.

Practice

1Fill in the blankCurriculum practice

Complete the condition: if people is 2 or more and points is 3000 or more, print 20% off.

Python Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor 
people = 3
points = 3500
if ___:
    print("20% off")
Console
Press Run to see the result.
2Write the programCurriculum practice

Set people to 2 and points to 3500. If people is 2 or more and points is 3000 or more, print Get an eco bag.

Python Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor 
  
 
Console
 
Press Run to see the result.
 
   
 
 
3Write the programCurriculum practice
 
Set age to 15. If age is 12 or less or 65 or more, print 30% off; otherwise print Full price.
  
 
 Python Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
  
 
Console
 
Press Run to see the result.
 
   
 
 
4Write the programCurriculum practice
 
Set age to 12 and people to 2. If age is 12 or less and people is 1 or more, print Child fare.
  
 
 Python Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
  
 
Console
 
Press Run to see the result.
 
   
 
 
5Fill in the blankCurriculum practice
 
Complete the condition: if the number of people is 10 or more or the total is 10000 or more, print Bonus Gift.
  
 
 Python Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
number_of_people = 4
total = 13500
if ___:
    print("Bonus Gift")
  
 
Console
 
Press Run to see the result.
 
   
 
 
6Write the programExtra practice
 
A student joins the competition if their maths mark is 85 or more and their attendance is 90 or more. With math = 88 and attendance = 86, print Accepted or Not accepted.
  
 
 Python Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
math = 88
attendance = 86

  
 
Console
 
Press Run to see the result.
 
   
 
 
7Write the programExtra practice
 
The school cancels the morning assembly if the temperature is 38 or more or rain is "yes". With temp = 31 and rain = "yes", print No assembly today; otherwise print Assembly at 8:00.
  
 
 Python Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
temp = 31
rain = "yes"

  
 
Console
 
Press Run to see the result.
 
   
 
 
Key points
  • A and B is true only when both conditions are true.
  • A or B is true when at least one is true.
  • Write a full condition on each side: age <= 12 or age >= 65.