Functions Practice

These questions follow Functions and Parameters, Returns, and Scope. A function is a named piece of thinking: information goes in through parameters, an answer comes back through return, and everything else stays inside.

Reading

1. In def letter_grade(mark):, called as letter_grade(78), name these four things: the definition, the parameter, the argument, and what return "B" does.
2. Predict the output.

   def double(number):
       print(number * 2)
    
   result = double(5)
   print(result)

3. Find the fault. This is supposed to give 69.5.

   def average(values):
       total = 0
       for value in values:
           total = total + value
       total / len(values)
    
   print(average([78, 91, 46, 63]))

4. Why does this fail, and what should the last line be instead?

   def total_of(values):
       total = 0
       for value in values:
           total = total + value
       return total
    
   total_of([1, 2])
   print(total)

Writing

5. Write kilograms_to_pounds(kilograms), which returns the mass in pounds (multiply by 2.2). Print the result for 6.5 kg to one decimal place.
6. Write is_overdue(days_late), which returns True or False. Show it being used directly inside an if.
7. Write greet(name, greeting="Hello") so that greet("Priya") and greet("Priya", "Welcome back") both work.
8. Challenge. These two lines appear in four places in a program:

   hours = minutes // 60
   rest = minutes % 60

   Turn them into a function, then write a second function that uses the first to produce Priya: 3 h 5 min.

Answers

Answer 1

def letter_grade(mark): is the definition; mark is the parameter, a name that only exists inside the function; 78 is the argument, the value supplied at the call; and return "B" hands "B" back to whoever called and ends the function immediately. Leave the argument out and Python is precise about it:

TypeError: letter_grade() missing 1 required positional argument: 'mark'

Answer 2

10, then None. The function prints but never returns, so result receives Python’s “no value at all”. A function that prints can only ever do that one thing; a function that returns can be stored, compared, or passed on.

Answer 3

The last line of the function computes the average and throws it away — there is no return, so the call produces None. Add it:

def average(values):
    total = 0
    for value in values:
        total = total + value
    return total / len(values)
 
print(average([78, 91, 46, 63]))

69.5

Answer 4

total is local to total_of — created when the function starts and gone when it ends:

NameError: name 'total' is not defined

The caller has to catch the returned value: print(total_of([1, 2])), which prints 3. That restriction is a feature: nothing outside the function can be damaged by what happens inside it.

Answer 5

def kilograms_to_pounds(kilograms):
    return kilograms * 2.2
 
print(f"{kilograms_to_pounds(6.5):.1f}")

14.3

The function returns the full-precision number; the rounding belongs at the point of display, not inside the calculation.

Answer 6

def is_overdue(days_late):
    return days_late > 0
 
if is_overdue(3):
    print("Send the reminder.")

days_late > 0 is already True or False, so there is no need to write if days_late > 0: return True. Naming a condition like this is the cheapest readability win in the language.

Answer 7

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}."
 
print(greet("Priya"))
print(greet("Priya", "Welcome back"))

Hello, Priya.
Welcome back, Priya.

A default value makes the second parameter optional. Defaults must come after the parameters that have none.

Answer 8

def as_hours_and_minutes(minutes):
    return f"{minutes // 60} h {minutes % 60} min"
 
def summary(name, minutes):
    return f"{name}: {as_hours_and_minutes(minutes)}"
 
print(summary("Priya", 185))

Priya: 3 h 5 min

The awkward arithmetic now exists once. When the coach asks for 3h05 instead, one function changes and every line of output follows — which is the entire argument for writing functions in the first place.