In this part, we are going to look at how to get the user to type something on their keyboard, and storing the result in a variable.
Create a new file, and call it user_input.py:
# Example of how to get user input from keyboard name = input("What is your name? ") print(f"Hello, {name}! Nice to meet you!") age = input("How old are you? ") # Use int() function to convert input to integer age = int(age) # age = int(input(...)) works too print(f"Oh I see, you're {age} years old.")
Answer to the exercise in Part 1
Let's start with showing the answer to the exercise from Part 1. Please note that you can solve the problem in many different ways, but this is one of the easiest ways of doing it. But don't worry if your version differs a bit from this one - the important part is that it works.
# Simple Hello world example (this is a comment). print("Hello world!") # Create some variables height = 42 width = 15 depth = 20 # Here, we add the depth variable # Calculate area by multiplying height with width area = height * width volume = height * width * depth # Calculate volume # Note the 'f' before the string in the following line. # It's why we can use {area} to print its value. print(f"The area is {area}.") print(f"The volume is {volume}.") # Print the volume
Now that we're done with that, let's move on to the meat of this part!
Reading user input
Let's create a new Python file, by opening IDLE and selecting File
and then New file. We will be calling this file user_input.py.
Technically, the name doesn't matter (other than the .py ending),
you can use whatever name you want. Once the window for this new file
is displayed, you can close the old window for our previous hello.py
program if it's still open.
Now, with this new user_input.py file, we are going to be accepting
user input - that is to say, we will ask the user something and store
their response in a variable. Type the following into our new file:
# Example of how to get user input from keyboard name = input("What is your name? ") print(f"Hello, {name}! Nice to meet you!")
As you can see, we're using a new function now called input. It
allows us to wait for the user to type something followed by the
Enter key, before program execution continues. Note the space after
"name?" above - without it, the cursor will appear right next to the
question mark, making things look very cramped.
We should also take note of the fact that program says name =
input(...). Previously, we've seen things like height = 42, which
makes a lot more sense. We want height to be 42. But what does name
= input(...) mean? To explain that, we have to take a bit of a closer
look at exactly what functions (such as print and input) really
are.
Functions and return values
Functions in Python are pieces of code that do something for us, so
that we don't have to do everything ourselves all the time. The
print function displays text, and the input function asks the user
to type something. Some functions, such as input, returns
something - they are said to have return values. In the case of
input, the "return value" is what the user typed. If I run the above
program and answer the "What is your name?" question with
"Enfors", then the return value of input is "Christer".
This may sound a bit confusing, but don't worry. It will soon become
clearer. For now, just think of it this way: If program says answer =
input("Please answer: "), then whatever the user typed in response,
will be stored in the variable answer.
Technically, all functions have return values. But some of them (for
example print) return a special value called None, which basically
means "nothing" - I have nothing useful to return.
Asking the user another question
Let's add some code to ask the user another question:
# Example of how to get user input from keyboard name = input("What is your name? ") print(f"Hello, {name}! Nice to meet you!") age = input("How old are you? ")
Great! When we have saved (Control-s) and ran (F5) the program, we
will have the user's age stored in a variable called age. There is,
however, a slight problem; the age is stored as the wrong variable
type - it is stored as what is known as a "string", rather than as a
number.
So what exactly is this "string" thing of which you speak? Allow me to explain. Consider, if you will, the following program:
print(1 + 2) # 1 and 2 are numbers - integers, to be exact print("1" + "2") # "1" and "2" are strings
If you were to run such a program, you would get the following result:
3
12
What's going on here? The first line, print(1 + 2), obviously worked
as intended. But the other one seems to think that one plus two is
twelve! This is strange, so let's experiment a bit. Let's say we tried
the following:
print("Hello" + "There")
Then we would get the following output:
HelloThere
And that makes sense, right? Because we're adding two words
together - "Hello" and "There" - so of course we get
"HelloThere". In Python terms, we says that "Hello" and "There"
are strings. They are not numbers. So what about "1" and "2",
with the quotation marks? They too are strings, precisely because of
the quotation marks. That means that 1 and 2 are numbers, and if
we add them we get 3. But "1" and "2" are strings - words! - and if
we add them together we get "12".
Okay, so back to our previous program, repeated here for clarity:
# Example of how to get user input from keyboard name = input("What is your name? ") print(f"Hello, {name}! Nice to meet you!") age = input("How old are you? ")
The function input always returns strings, such as "Enfors" or
"43", even if we type in numbers when we run it. But that's a
problem we can handle by using a new function we haven't talked about
before - the int function. The int function can take a string
variable and convert it to an integer - a number. Let's do just that,
also remembering to add a comment to explain what we're doing. While
we're at it, we'll also add another print to display the age that
the user typed:
# Example of how to get user input from keyboard name = input("What is your name? ") print(f"Hello, {name}! Nice to meet you!") age = input("How old are you? ") # Use int() function to convert input to integer age = int(age) print(f"Oh I see, you're {age} years old.")
In the same way that the input function "returns" what the user
types, the int function "returns" an integer. So just having
int(age) in our program is not enough, because then we're not
storing the return value (the number). That's why we need to type age
= int(age). Then we're grabbing what the function int returns, and
storing it in our age variable.
Now when we save (Control-s) and run (F5) our program, we get the
following result:
What is your name? Enfors
Hello, Enfors! Nice to meet you!
How old are you? 43
Oh I see, you're 43 years old.
Let's combine what we've learned in this part with what we learned in Part 1. Write a program that asks the user for a height and a width, remembering to convert them into integers. Then, calculate the area and display it. You will get an example of how to do it in the next part.
Previous: Part 1: Introduction | Next: Part 3: If statements and indentation | Index