print in Python: displaying messages on screen

Hey there! In this article, we’ll talk about the print function in Python. This function is handy for showing messages on the screen or saving them in a file. We’ll discuss how to utilize this function in depth, along with its differences in Python 3 compared to Python 2.

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Displaying messages on screen in Python 3

To show a message on the screen in Python 3, you can use the built-in print function:

print("Hello, world!")

Output:

Hello, world!

Displaying messages on screen in Python 2

In Python 2, you use the print keyword, not the function:

print "Hello, world!"

Output:

Hello, world!

For the rest of the article, we’ll focus mainly on the print function in Python 3. If you’re curious about print in Python 2, I’d recommend checking out the official documentation.

The print function

The print function in Python looks like this:

print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

• First, we pass the objects we want to display. The print function will automatically turn these into strings. The asterisk indicates that we can pass any number of values.
• By default, all values are shown separated by a space. To change the separator, use sep='your separator'.
• After all the objects are displayed, print will move to the next line. You can adjust what’s shown at the end by using the end argument.
• By default, the message will show on the screen. But, if you want to direct it to a file, use the file argument.
• flush determines whether the message appears right after calling the function or if it waits a bit. Messages usually aren’t shown immediately after calling because programs run faster that way. If you want to ensure the message appears immediately after using print, set flush=True.

Now, let’s see how each of these arguments works individually.

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Displaying multiple values

print lets you show multiple values in one message:

print("I", "went", "for a walk")

Output:

I went for a walk

And we’re not limited to just strings:

print("2 * 3 =", 6)

Output:

2 * 3 = 6

The print function will convert any value you give it into a string. Let’s try showing the print function using print itself:

print('print:', print)

Output:

print: <built-in function print>

Here, we see that print is a built-in function in Python.

How to change the separator in print

To change the space with something else when printing multiple values, you can use the sep parameter:

print(1, 2, 3, sep=", ")

Output:

1, 2, 3

Here, we’ve displayed numbers separated by a comma and a space. You can choose any separator that fits your needs.

How to change the print ending

By default, print starts a new line after each print statement:

print("First line")
print("Second line")

Output:

First line
Second line

You can adjust what gets printed at the end of a message by using the end argument:

print("One |", "Two", end=" | ")
print("Three")

Output:

One | Two | Three

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Writing messages to a file

To write a message to a file, print has a special parameter named file. Let’s try printing the message “Hello World!” to a file called output.txt:

with open("output.txt", "w") as f:
    print("Hello World!", file=f)

output.txt:

Hello World!

In the example above, we’re using the open function to open a file for writing. Once the file is opened, you just pass it to the file parameter of the print function.

Flushing the print output with flush

Before we jump into flushing the print output, let’s demonstrate the fact that messages don’t always show up on the screen immediately:

import time

print("Message #1", end=", ")
time.sleep(3)
print("message #2")

I’d recommend running this code on your computer to see it in action. But in any case, here’s what’ll happen:

1. For the first three seconds, you won’t see anything on the screen, even though print has been called.
2. After three seconds, the second call to print will flush the waiting output to the screen.

You’ll end up seeing:

Message #1, message #2

To see the first message right away, without waiting for the second print, you can set flush=True. This will prompt Python to display “Message #1, ” without waiting for the next print call:

import time

print("Message #1", end=", ", flush=True)
time.sleep(3)
print("message #2")

By default, Python displays a message on screen after a newline character '\n'. That’s why, to demonstrate the flush parameter, we changed the end for the first message to a comma.

Example: printing an integer

As we’ve seen, to print numbers using the print function, you can simply pass the number:

number = 1
print(number, 2)

Output:

1 2

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Example: displaying a string on the screen

You can easily pass a string as a parameter to the print function to display it:

print("Displaying a string in Python")

Output:

Displaying a string in Python

Example: displaying a list in Python

To display a list, you can simply pass it to the function. In this case, print will show the list items separated by commas within square brackets:

l = [1, "two", 3]

print(l)

Output:

[1, 'two', 3]

If you need to display the items differently, you can do it manually:

l = [1, "two", 3]
for index, item in enumerate(l):
    print(item, end="")
    if index == len(l) - 1:
        print() # new line
    else:
        print(" | ", end="") # custom delimiter

Output:

1 | two | 3

But the example above is a bit verbose. It’s easier to use the join method:

l = [1, "two", 3]
print(" | ".join(str(x) for x in l))

Output:

1 | two | 3

Here, we first converted all list elements to strings using a generator and then joined them using join.

Example: displaying a dictionary using print

The print function can also beautifully display dictionaries:

d = {"A": 1, "B": 2}
print("Dictionary:", d)

Output:

Dictionary: {'A': 1, 'B': 2}

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Example: displaying a set in Python

You can also display sets using the print function:

s = {1, 2, 3}
print("Set:", s)

Output:

Set: {1, 2, 3}

Exercises

1. Using print:
   Write a Python program that asks the user for their name and displays a welcome message on the screen using the print function.
2. Writing to a file using print:
   Create a text file named “output.txt”. Write a program that uses the print function to write the string “Hello, world!” to this file. After executing the program, open the file to ensure the string was written correctly.
3. Managing delimiters and line endings in print:
   Write a program that showcases the ability to use various delimiters and line-ending characters in the print function. Try changing the default delimiter (space) and default line ending (new line) to something else, and display multiple values on the screen.