Functions and Modules Answers

Module Exercises

Allow Zero Arguments

Make a script like our greetings.py file, but allow it to take zero arguments. When no arguments are given, it should say “Hello world!”

Answers

import sys

arguments = sys.argv[1:]
if __name__ == "__main__":
    if arguments:
        name = arguments[0]
    else:
        name = "world"
    print("Hello {}!".format(name))

CLI Only

Make a module that prints “Hello world” when you use it from the command-line, but prints an error message when you try to import it. It should work like this:

$ python hello.py
Hello world

>>> import hello
This module can only be run from the command-line

For bonus points, make the module raise an error when importing instead of just printing a message. You can use this line to raise this error:

>>> raise ImportError("This module can only be run from the command-line")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: This module can only be run from the command-line

Answers

if __name__ == "__main__":
    print("Hello world!")
else:
    raise ImportError("This module can only be run from the command-line")

Add

Make a program add.py that takes two numbers and prints out the sum of these numbers.

$ python add.py 3 5.2
8.2
$ python add.py -7 2
-5.0
$ python add.py -2 -1
-3.0

Answers

import sys

print(float(sys.argv[1]) + float(sys.argv[2]))

Difference Between

Make a program difference.py that takes two numbers and prints the positive difference between these two numbers:

$ python difference.py 3 5
2.0
$ python difference.py 6 3.5
2.5
$ python difference.py -7 2
9.0

Answers

import sys

print(abs(float(sys.argv[1]) - float(sys.argv[2])))

Allow Unlimited Arguments

Make a script like our greetings.py file that takes any number of arguments. All arguments should be joined together by spaces and printed out.

Your script should work like this:

$ python greetings.py
Hello!
$ python greetings.py world
Hello world!
$ python greetings.py from planet Earth
Hello from planet Earth!

Tip

You may have noticed we did this in an example earlier, but you can get a list of all arguments with sys.argv[1:]. We’ll explain how this works in the next class.

Hint

Use str.join on the sys.argv list.

Answers

import sys

arguments = sys.argv[1:]
if __name__ == "__main__":
    if arguments:
        print("Hello {}!".format(" ".join(arguments)))
    else:
        print("Hello!")

Function Exercises

Hypotenuse

Make a function that returns the hypotenuse of a right triangle given the other two sides. Your function should work like this:

>>> get_hypotenuse(3, 4)
5.0
>>> get_hypotenuse(5, 12)
13.0

Hint: to get the square root of a number, raise it to the power of 0.5.

Answers

def get_hypotenuse(x, y):
    return (x ** 2 + y ** 2) ** 0.5

To Celsius

Make a function that accepts a temperature in Fahrenheit and returns a temperature in Celsius.

>>> to_celsius(212)
100.0

Answers

def to_celsius(fahrenheit):
    return (fahrenheit - 32) * 5 / 9

Is Leap Year

Make a function that takes a year and returns True if and only if the given year is a leap year.

• Leap years are years that are divisible by 4
• Exception: centennials (years divisible by 100) are not leap years
• Exception to exception: years divisible by 400 are leap years

You may find this pseudocode from Wikipedia helpful.

Answers

def is_leap_year(year):
    if year % 4:
        return False
    elif year % 400 == 0:
        return True
    elif year % 100 == 0:
        return False
    else:
        return True

Perfect Square

A perfect square is a number which is the square of an integer. For example 25 (5 * 5), 49 (7 * 7) and 81 (9 * 9) are all perfect squares.

Make a function that returns True if the given number is a perfect square.