Printing

2. Basic Types: Strings

Printing

We have already seen a lot of output in the previous exercises, but this is not how Python programs would normally behave. If we were to write expressions in a Python file and run it, we would see no output at all. In order for your more complex programs to output anything you will have to use the built-in function $\color{#8959A8} {\mathtt{\text{print}}}$ .

A built-in function is a function that is directly built in the Python source code and thus immediately available to the programmer.

Built-in functions are provided by the Python developers because they generally perform some action that is used extensively by developers, like displaying data. We will gradually see more and more built-in functions throughout this course, but if you want to already take a look at all the built-in functions Python 3 provides, visit the official documentation.

The $\color{#8959A8} {\mathtt{\text{print}}}$ function will likely be the built-in function you will use the most in your Python endeavor. While there are other methods to display output, the $\color{#8959A8} {\mathtt{\text{print}}}$ function is the most concise way to have your Python programs output anything. It is defined as follows:

Function Definition
$\color{#8959A8} {\mathtt{print}}(\textit{object}_\textit{1}, \textit{object}_\textit{2}, \text{. . .} )$

Where the $\textit{object}$ arguments can be of any Python type, such as numbers, strings or variables.

The complete definition of the $\color{#8959A8} {\mathtt{\text{print}}}$ function is actually as follows:
$\color{#8959A8} {\mathtt{print}}(\textit{object}_\textit{1}, \textit{object}_\textit{2}, \text{. . .}, \mathtt{\text{sep}\color{#3e999f} {\text{=}}\color{#718c00}{\text{" "}}}, \mathtt{\text{end}\color{#3e999f} {\text{=}}\color{#718c00} {\text{"}}\color{#F5871F}{\text{\n}}\color{#718c00} {\text{"}}}, \mathtt{\text{file}\color{#3e999f} {\text{=}}\text{sys.}\color{#4271ae}{\text{stdout}}}, \mathtt{\text{flush}\color{#3e999f} {\text{=}}\color{#F5871F}{\text{False}}} )$
It provides four additional optional arguments in $\mathtt{\text{sep}}$ , $\mathtt{\text{end}}$ , $\mathtt{\text{file}}$ and $\mathtt{\text{flush}}$ . These arguments have default values specified after $\mathtt{\text{=}}$ per the definition of the function. The default values can be modified to achieve different behaviour, $\mathtt{\text{sep}}$ specifies the string used to separate the resulting strings and $\mathtt{\text{end}}$ specifies the string appended to the end of the line, they are set to space $\color{#718c00} {\mathtt{\text{" "}}}$ and the newline character $\mathtt{\color{#718c00} {\text{"}}\color{#F5871F} {\text{\n}}\color{#718c00} {\text{"}}}$ by default. The function of the $\mathtt{\text{file}}$ and $\mathtt{\text{flush}}$ arguments is beyond the scope of this course.

The $\color{#8959A8} {\mathtt{\text{print}}}$ function converts its arguments to $\color{#4271ae} {\mathtt{\text{str}}}$ objects and prints them on the same line separated by spaces. The $\color{#8959A8} {\mathtt{\text{print}}}$ function automatically forces a new line after all the arguments are printed. This is accomplished by appending the newline character $\color{#F5871F} {\mathtt{\text{\n}}}$ to the end of the line. When no arguments are provided, only the newline character is printed. The newline character is an example of an escape sequence.

An escape sequence is a sequence of one or multiple characters preceded by a backslash that is not evaluated literally when printed.

In addition to the newline character, other potentially useful escape sequences include:

$\mathtt{\text{\t}}$
$\mathtt{\text{\b}}$
$\mathtt{\text{\"}}$
$\mathtt{\text{\'}}$
$\mathtt{\text{\\}\text{\\}}$

Evaluates to ASCII tab.
Evaluates to ASCII backspace.
Evaluates to literal $\mathtt{\text{"}}$ .
Evaluates to literal $\mathtt{\text{'}}$ .
Evaluates to literal $\mathtt{\text{\\}}$ .

>>> print("\tA tab.\n\t\tTwo tabs.")

A tab.
Two tabs.

>>> print("He's a \"developer\".")

He's a "developer".

>>> print('He\'s a "developer".')

He's a "developer".

Let's take a look at some examples of $\color{#8959A8} {\mathtt{\text{print}}}$ function usage:

Calling $\color{#8959A8} {\mathtt{\text{print}}}$ with a single $\color{#4271ae} {\mathtt{\text{str}}}$ object as argument:

>>> print("Hello!")

Hello!

Calling $\color{#8959A8} {\mathtt{\text{print}}}$ with a $\color{#4271ae} {\mathtt{\text{str}}}$ and an $\color{#4271ae} {\mathtt{\text{int}}}$ object as arguments:

>>> print("The answer?", 44)

The answer? 44

Calling $\color{#8959A8} {\mathtt{\text{print}}}$ with a predefined variable:

>>> var = "eggs"
>>> print(var)

eggs

Using the optional $\mathtt{\text{sep}}$ argument we can achieve more complex formatting, like so:

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

1, 2, 3

Or so:

>>> print("First", "Second", "Third", sep="\n")

First
Second

Third

Additionally, we can use the optional $\mathtt{\text{end}}$ argument to control what is appended to the end of the output of a single $\color{#8959A8} {\mathtt{\text{print}}}$ call:

>>> print("A sentence", "Another sentence", sep=". ", end=".\nThe end.\n")

A sentence. Another sentence.
The end.

Combining the $\color{#8959A8} {\mathtt{\text{print}}}$ function with the previously discussed string formatting techniques is a very useful way to preserve the readability of your code in addition to the readability of its output.