Elif Statement

Sometimes we may wish to use an alternative test should our previous test evaluate as False.

elif which is short for else if, lets us do exactly that.

1. Using the Elif Statement

We can test another condition after the first condition as follows:

1.1 Example - if ... elif

Remember from Nested If Statements that we can do the following:

# change these to experiment with the if..elif block
x = 4
y = 5

if x < y:
  # block of code
  print("x is less than y")
elif x > y:
  # block of code
  print("x is greater than y")

Here depending on the values of x and y one (and only one) of the print statements is executed.

If x is less than y then x < y is True and the first block is executed.

If x is greater than y then x < y is False and the elif part is checked. As x > y is True, the second block is executed.

What about if x and y are equal?

Copy the code above into a Python file and experiment with different values of x and y.

1.2 Example - if ... elif ..else

We can also include an else statement, now our program will output when x and y are equal.

# change these to experiment with the if..elif..else block
x = 4
y = 5

if x < y:
  # block of code
  print("x is less than y")
elif x > y:
  # block of code
  print("x is greater than y")
else:
  # block of code
  print("x is equal to y")

You should think about this and realise that there are three possibilities.

1. x is less than y
2. x is greater than y
3. x is equal to y

If the first two are False, then it must be that x is equal to y. We don't need a test, we can just the else statement.

1.3 The Connection with if ... else

The program from the last section:

# change these to experiment with the if..elif..else block
x = 4
y = 5

if x < y:
  # block of code
  print("x is less than y")
elif x > y:
  # block of code
  print("x is greater than y")
else:
  # block of code
  print("x is equal to y")

Can be rewritten in terms of just if and else statements:

# change these to experiment with the if..elif..else block
x = 4
y = 5

if x < y:
  # block of code
  print("x is less than y")
else:         # You can see from these two lines where elif gets it's name, it is doing the same as else if!
  if x > y:
    # block of code
    print("x is greater than y")
  else:
    # block of code
    print("x is equal to y")

1.4 Example - Multiple elif statements

Another example is testing to see if the first letter of someone's name begins with a vowel.

input_name = input("Please enter your name:\n")

# convert the name to lowercase
name = input_name.lower()

if name[0] == "a":
  print("The name begins with an a")
elif name[0] == "e":
  print("The name begins with an e")
elif name[0] == "i":
  print("The name begins with an i")
elif name[0] == "o":
  print("The name begins with an o")
elif name[0] == "u":
  print("The name begins with an u")
else:
  print("The name does not begin with a vowel")

I suggest trying each of these programs out in Python.

Note that this is not the most efficient way to do this, we can either use the newer match statement available since Python 3.10 (version). We could also do a similar thing using lists

=== TASK ===

Write a program that outputs whether a number is positive, negative, or zero. Your program should accept numbers of type float.

• If the number is positive it should output Your number is positive!
• If the number is negative it should output Your number is negative!
• If the number is zero it should output Your number is zero!  

For example, your program should output the following given these inputs:

Please enter a number:
2.3
Your number is positive!

Please enter a number:
-3.3
Your number is negative!

Please enter a number:
0
Your number is zero!