After reading lesson 11, you’ll be able to
- Print values for the user
- Ask the user for input
- Store user input in variables and do operations with it
Many programs are written to do computations behind the scenes, but few of them are useful without some sort of input from a user. One main reason you’d want to write a program is to provide users with a certain experience; that experience relies on a back-and-forth between the user and the program.
Consider this
Find another person and have a conversation. What kinds of questions can you ask? What responses do you get? Can you build upon a specific response you get?
Answer:
- How are you?
- Good, looking forward to the weekend.
- Me too! Any weekend plans?
- Yes, we’re going camping, then checking out the science museum. If we have time, maybe hit the beach and then going out for a nice dinner. You?
- Watching TV.
To get started with this lesson, recall that you can use the print() command to show the user values on the console in Python. You’ll use print a lot from now on.
You can put any expression inside the parentheses of print(), because all expressions evaluate to a value. For example, the float 3.1 has a value 3.1, and the expression 3 * "a" has a value "aaa".
Listing 11.1 shows how to print the values of a few expressions to the user. You can have fairly complex expressions in the parentheses. The code in this listing prints out the following:
hello! 89.4 abcdef ant
Listing 11.1. Printing expressions
print("hello!") #1
print(3*2*(17-2.1)) #2
print("abc"+"def") #3
word = "art" #4
print(word.replace("r", "n")) #5
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Quick check 11.1
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1 / 2 = 0.5 1/2=0.5
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Listing 11.2. Printing multiple objects
a = 1 #1 b = 2 #1 c = a/b #2 print(a,"/",b,"=",c) #3 add = str(a)+"/"+str(b)+"="+str(c) #4 print(add) #5
Quick check 11.2
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input("What's your name? ")
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What's your name?
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Quick check 11.3
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Listing 11.3. Where does the user live?
input("Where do you live? ") #1
print("I live in Boston.") #2
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Listing 11.4. Storing the user input
user_place = input("Where do you live? ") #1
text = user_place.capitalize() + "!" #2
print(text) #3
print("I hear it's nice there!") #3
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Quick check 11.4
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Listing 11.5. Calculations with user input
user_input = input("Enter a number to find the square of: ") #1
num = int(user_input) #2
print(num*num) #3
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Listing 11.6. Calculations with more than one user input
num1 = float(input("Enter a number: ")) #1
num2 = float(input("Enter another number: ")) #2
print(num1, "*", num2, "=", num1*num2) #3
In this lesson, my objective was to teach you how to show output and how to get input from the user. You learned that you can print multiple objects by using only one print statement and that Python automatically adds a space between each object.
You learned about using the input() command to wait for user input. The command converts anything that the user enters into a string object. If you want to work with numbers, you have to convert the input to an appropriate type yourself in the program code. Here are the major takeaways:
- print can be used on multiple objects in one go.
- You can ask the user for input as many times as you want. Each time, the program halts and waits for the user to enter something, and users indicate that they’re done by pressing the Enter key.
- You can convert the user input into other types to do appropriate operations on it.
Write a program that asks the user for two numbers. Store these numbers in variables b and e. The program calculates and prints the power be with an appropriate message.
Write a program that asks the user’s name and then age. Use appropriate variable names to store these variables. Calculate how old the user will be in 25 years. For example, if the user enters Bob and 10, the program should print Hi Bob! In 25 years you will be 35!