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More Data Types

Today we will continue talking about things we can do with numbers and strings in Python. We will go over a couple examples of doing math in programs, then a few more operations on both sorts of data.

Finally, we'll talk about another type of data, the boolean.


Example: Tax

How could we write a program which asks the user for the cost of an item and then applies a 5% sales tax. The program should print the full cost of the item with tax.


cost = int(input("How much is the item?" )

total = cost * 1.05
print("The total cost is", total)


Example: Circle Computation

How could we write a program which will take in the radius of a circle, and print out the area and circumference?

The formulas for these are:

$A = \pi R^2$

$C = 2 \pi R$


# get input
radius = int(input("What is the radius of the circle? " )

# do the area
area = 3.1416 * (radius ** 2)
print("The area is", area)

# do the circumference
circum = 2 * 3.1416 * radius
print("The circumference is", circum)


More on Strings

A string is a sequence of one or more characters. A character is just a single symbol of text, such as a letter, numeral, punctuation or space. For instance, the string string "Hello World!" has 12 characters: 10 letters, a space, and an exclamation mark.

We can get the length of a string by using the len command. The following program will get a string from the user and then print how long it is:


response = input("Enter a string: ")
length = len(response)
print("That string has", length, "characters.")

We can also get any individual characters out of a string if we want to. Each character in a string has an index. The index starts at 0 and goes up by 1 for each character. For instance, the string "Hello" has these indices:


The indices of a string

To get just one character from a string, we put the name of the string, then the index we want inside square brackets.

For example, we can write a program that prints out the first letter of our input like this:


response = input("Enter a string: ")
first = response[0]
print(first)

How could we get the last character of a string to print out?


response = input("Enter a string: ")
length = len(response)
last = response[length - 1]
print(last)


Rounding

Sometimes our tax calculator program above will print prices that don't stay in the normal 2 decimal places of money values. For instance, if we pass 3.67, it will return 3.8535.

In order to fix this, we can round the result to 2 decimal places. This is done with the round command, which takes the number we want to round and how many decimal places to round to:


>>> round(3.8535, 2)
3.85

round always rounds to the nearest place. For instance round(4.7, 0) rounds up to 5, while round(4.3, 0) will round down to 4.

Copyright © 2018 Ian Finlayson | Licensed under a Creative Commons Attribution 4.0 International License.