Writing to the Screen

Note

Source: Drawn from the SE4ML Python chapter (chapter_python.rst, lines 753–780) and adapted from the C# edition (data/print1.rst). The sep= and end= keyword arguments are Python-specific additions.

The primary way to produce output in Python is the built-in print function.

Basic Use

Pass print a string and it writes that string to the screen, followed by a newline:

>>> print("Hello, world!")
Hello, world!

You can print the value of any expression:

>>> print(2 + 3)
5
>>> total = 42
>>> print(total)
42

Multiple Arguments

print can take multiple arguments, separated by commas. It writes them separated by spaces:

>>> print("The answer is", 42)
The answer is 42
>>> print(1, 2, 3)
1 2 3

You can change the separator with the sep keyword argument:

>>> print(1, 2, 3, sep=", ")
1, 2, 3
>>> print("cat", "dog", "bird", sep=" | ")
cat | dog | bird

Controlling the End Character

By default, print adds a newline after the last value. You can change this with the end keyword argument. To suppress the newline entirely, use end="":

print("Enter your name: ", end="")

This is useful when you want user input to appear on the same line as the prompt. (The input() function handles this automatically, as we will see in Combining Input and Output, but print with end="" is needed in other situations.)

To print several items on the same line in separate print calls:

>>> print("one", end=" ")
>>> print("two", end=" ")
>>> print("three")
one two three

Printing Nothing

A print() with no arguments writes a blank line:

>>> print("Before")
>>> print()
>>> print("After")
Before

After

This is useful for adding vertical space in output.

Printing to a File

print can write to a file instead of the screen using the file keyword argument:

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

We will cover file I/O in the Files chapter.