Review: Functions

Module 1: Python Fundamentals

Review of Session 1.4: Functions

Exercise

Without running the code, what is going to be the output of this cell?

def yell(text="hello"):
  print(text.upper() + "!")

::: {.callout-tip collapse=“true”} ## Solution Some variants:

:::
# Same as above, with type hints
def yell(text: str="hello"):
  print(text.upper() + "!")

# What if we use return?
def yell(text="hello"):
  return text.upper() + "!"

# When using return, the function "yell()" outputs a string
# We can concatenate that string to another
print(yell() + " CLASS!")

Exercise

Without running the code, what is going to be the output of this cell?

def powers_of_number(n, limit=4):
  for x in range(1, limit):
    print(f"{n}^{x} = {n**x}")

powers_of_number(2)

# Same as above, with type hints
def powers_of_number(n: int, limit: int=4):
  for x in range(1, limit):
    print(f"{n}^{x} = {n**x}")

powers_of_number(2)

Exercise

Look at the following piece of code and explain why it fails.

# Ask the user for a password until it gets it right
password = "coconout"

while user_input != password:
  user_input = input("Enter a password: ")

print("Access granted!")

::: {.callout-tip collapse=“true”} ## Solution Answer: We need to define the variable user_input before performing the comparison user_input != password.

Fixed:

:::
# Ask the user for a password until it gets it right
password = "coconout"

user_input = input("Enter a password: ")

while user_input != password:
  user_input = input("Enter a password: ")

print("Access granted!")

Exercise

Look at the following piece of code and explain why it fails.

# This code computes the sum of the first N natural numbers
n = input("Enter a positive integer: ")
print(f"The sum of the first {n} natural numbers is...")

while n > 0:
    result += n  # result = result + n
    n -= 1  # n = n - 1

print(result)

Solution

Answer: Same as before, we need to initialize the variable result before we start the while loop.

Exercise

Look at the following piece of code and explain why it fails.

# Exercise 4.6
# Define a function rectangle_area(length, width) that calculates the area of
# a rectangle based on its length and width.

def rectangle_area(length, width):
  return len * width

print(rectangle_area(10, 20))

# Exercise 4.6
# Define a function rectangle_area(length, width) that calculates the area of
# a rectangle based on its length and width.

def rectangle_area(length, width):
  return length * width


length = 20
width = 40
rectangle_area = rectangle_area(length, width)
print(rectangle_area)

length_2 = 10
width_2 = 20
rectangle_area_2 = rectangle_area(length_2, width_2)
print(rectangle_area_2)

print = "Hello world"

print(print)

print(8)

::: {.callout-tip collapse=“true”} ## Solution Answer: The name of the variable we are using is length, not len! In fact, len is reserved to be the name of a Python built-in function.

:::
# Same as above, with type hints
def rectangle_area(length: float, width: float) -> float:
  return len * width

print(rectangle_area(10, 20))

Exercise

Look at the following piece of code and explain why it fails.

# Exercise 4.19
# Define a function circle_area(radius, is_diameter=False) that calculates
# the area of a circle based on its radius.
# If the keyword argument is_diameter is input as True,
# then the function considers that radius is instead the diameter

def circle_area(radius, is_diameter = False):
  # Compute for radius
  return 3.1415 * radius**2

  # Correction for diameter
  if is_diameter:
    radius = radius / 2
    return 3.1415 * radius**2


print(circle_area(10))  # Expected output: 314.15
print(circle_area(10, is_diameter=True))  # Expected output: 78.54

# Exercise 4.19
# Define a function circle_area(radius, is_diameter=False) that calculates
# the area of a circle based on its radius.
# If the keyword argument is_diameter is input as True,
# then the function considers that radius is instead the diameter

def circle_area(radius, is_diameter = False):
  # Correction for diameter
  if is_diameter:
    radius = radius / 2
    return 3.1415 * radius**2
  else:
    # Compute for radius
    return 3.1415 * radius**2

print(circle_area(10))  # Expected output: 314.15
print(circle_area(10, is_diameter=True))  # Expected output: 78.54

::: {.callout-tip collapse=“true”} ## Solution Answer: The return statement will finish the function right at the start. The if clause will never happen because of that return. We need to include an if clause when is_diameter is False.

:::
# Same as above, with type hints
def circle_area(radius: float, is_diameter: bool = False) -> float:
  # Compute for radius
  return 3.1415 * radius**2

  # Correction for diameter
  if is_diameter:
    radius = radius / 2
    return 3.1415 * radius**2


print(circle_area(10))  # Expected output: 314.15
print(circle_area(10, is_diameter=True))  # Expected output: 78.54

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