Advanced work with the print() function

10.1 format()

We often need to output a lot of data to the console (on the screen). We're definitely not the first to deal with this — which is why Python has had the function format() for a while now, and it lets you combine strings and display data on the screen way easier and more understandably.

The format() function is used to insert values into a string at specific positions. The syntax of the function looks like this:

"String template from {} to {}".format(value1, value2,…)

Fact 1. The function format() — is a string method, so it's called on a string. Instead of passing a string to the function, we write the string, put a dot, and then call the format() function, passing its parameters into it.

Fact 2. The function format() fills the string template with the passed values. It converts passed values into strings (if there were numbers, for example) and inserts them into places marked by {}. Such a place for inserting a value is called a placeholder.

Basic usage:

welcome_message = "Hello, {}, welcome to {}!"
print(welcome_message.format("Anna", "our store"))               
        

Result: "Hello, Anna, welcome to our store!"

Number formatting:

output = "Data: {0:.2f} and {1:.2f}".format(3.1415926, 2.71828)
print(output)              
        

Result: "Data: 3.14 and 2.72" — demonstrating output restricted to two decimal places.

Using keywords:

output = "{name} works at {company}"
print(output.format(name="Sergey", company="Google"))
        

Result: "Sergey works at Google"

Using format() enhances the readability and maintainability of the code, allowing you to easily change the format without having to edit the entire string.

10.2 f-notation

Starting with version 3.6, Python introduced a new type of string — f-strings, which literally mean "formatted string". These strings improve the readability of the code and run faster than other formatting methods.

To use f-strings, just put the letter "f" or "F" before a string. Expressions to embed are placed in curly braces {}:

Example:

force = "Dark Side"
message = f"May the force be with you {force}!"
print(message)  # Outputs: May the force be with you Dark Side! 
        

Note! Inside the curly brackets, you can include variables that are accessible in the current scope (more on that later) and Python will automatically convert them to a string and put them in the desired location.

Example:

age = 28
message = f"I am {age} years old"
print(message)  # Outputs: I am 28 years old               
        

Plus, you can use expressions with a bunch of variables inside the curly brackets.

Example:

birth_year = 1985
current_year = 2024
message = f"I am {current_year - birth_year} years old"
print(message)  # Outputs: I am 39 years old
        

Under the hood, it all gets converted to a call to format(), but the new approach is really more convenient.

Enjoy using it to your heart's content.

10.3 Parameters sep and end

In Python, the function print() offers two handy parameters — sep and end, which allow you to control the output of data. These parameters make the print() function more flexible and can be used for output formatting without needing additional functions or complex string operations.

The parameter sep defines the character or string that will be used to separate multiple values passed to print(). By default, sep is set as a space. This means if you pass multiple arguments to print(), they'll be separated by a space.

But if you want the data to be separated by, for instance, a comma, just add the parameter sep at the end and immediately assign it a new separator string.

Example:

            print("Hello", "world")  # Output: Hello world 
            print("Hello", "world", sep=", ")  # Output: Hello, world
        

Or, for example, you can make each value appear on a new line. Then, assign the sep parameter the special newline character — denoted by “\n”.

print(1, 2, 3, 4, 5, sep=",\n")  

The loop will output
1,
2,
3,
4,
5
            

The parameter end defines what will be printed after all the passed values. The default value for end is the newline character (\n), meaning it moves to a new line after executing print().

By changing end, you can control how data is printed, for instance, to continue output on the same line:

Example:

            print("Hello", end=" ")
            print("world")  # Output: Hello world               
        

Using sep and end can be incredibly useful in scenarios where specific output formatting is required, such as creating tables, reports, or when showing data in a single line without auto-line-breaks.

Aside from simplifying the code and avoiding the need to manually add separators or manage line breaks, using sep and end improves the readability and maintainability of the code.

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Python SELF EN, level 4, lesson 4

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F-notation

F-notation

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Python SELF EN, level 4, lesson 4

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From sep to end

From sep to end

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