{"id":17349,"date":"2020-11-24T22:42:10","date_gmt":"2020-11-25T06:42:10","guid":{"rendered":"https:\/\/careerkarma.com\/blog\/?p=17349"},"modified":"2023-12-01T04:04:57","modified_gmt":"2023-12-01T12:04:57","slug":"python-f-string","status":"publish","type":"post","link":"https:\/\/careerkarma.com\/blog\/python-f-string\/","title":{"rendered":"Python f Strings: The Ultimate Guide"},"content":{"rendered":"\n

Python f strings embed expressions into a string. An expression may be the contents of a <\/em>variab<\/em>le or the result of a mathematical calculation, or another Python value. f strings are distinguished from regular strings as the letter f comes before the string.<\/em><\/p>\n\n\n\n

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When you\u2019re writing a string, you may want to change part of a string to use a specific value. For instance, you may want a string to appear that contains the value the user has inserted into the console.\n\n<\/p>\n\n\n\n

Python has supported string formatting for a while, but Python 3.6 introduced a new method of changing strings to include new values: f strings.\n\n<\/p>\n\n\n\n

This tutorial will discuss, with reference to examples, the basics of f strings in Python. By the end of reading this tutorial, you\u2019ll be an expert at using Python f strings.\n\n<\/p>\n\n\n\n

Python String Formatting<\/h2>\n\n\n\n

Prior to Python 3.6, there were two ways you could format Python string<\/a>. You could use the percentage (%) formatting, and str.format()<\/em>.\n\n<\/p>\n\n\n\n

Percentage Formatting<\/h3>\n\n\n\n

Percentage formatting has been around since the beginning and allows you to format a string with one or multiple values.<\/p>\n\n\n\n

Here\u2019s an example of the percentage formatting approach in action:<\/p>\n\n\n\n

email = "lindsay.ballantyne@gmail.com"\nnew_string = "Your email address is %s." % email\nprint(new_string)<\/pre><\/div>\n\n\n\n
Our code returns:<\/p>\n\n\n\n
Your email address is lindsay.ballantyne@gmail.com<\/pre><\/div>\n\n\n\n
In our code, we use the %s sign as a placeholder for our new string in the \u201cYour email address is %s.\u201d string. At the end of that line of code, we use a percentage sign followed by \u201cemail\u201d to replace %s with our user\u2019s email address.<\/p>\n\n\n\n
str.format()<\/h3>\n\n\n\n
In Python 2.6, a new method of formatting strings was introduced: the format()<\/em> function.\n\n<\/p>\n\n\n\n
Suppose we want to format a string with two values. We could do so using the format()<\/em> method like so:<\/p>\n\n\n\n
name = "Lindsay Ballantyne"\nemail = "lindsay.ballantyne@gmail.com"\nnew_string = "Hello, {}. Your email address is {}.".format(name, email)<\/pre><\/div>\n\n\n\n
Our code returns:<\/p>\n\n\n\n
Hello, Lindsay Ballantyne. Your email address is lindsay.ballantyne@gmail.com.<\/pre><\/div>\n\n\n\n
In our code, we define two Python variables<\/a>, \u201cname\u201d and \u201cemail\u201d. These variables store the name and email address of someone using our program. Then, we use the .format()<\/em> syntax to add in the values \u201cname\u201d and \u201cemail\u201d to our string.<\/p>\n\n\n\n
Python f String Format<\/h2>\n\n\n\n
Python f strings embed expressions into a string literal. You can use f strings to embed variables, strings, or the results of functions into a string. An f string are prefixed with “f” at the start, before the string iitself begins.<\/p>\n\n\n\n
Introduced in Python 3.6, make it easier to format strings. <\/p>\n\n\n\n
f strings<\/em> use curly braces to store the values which should be formatted into a string. f strings can also use a capital \u201cF\u201d to represent a formatted string.<\/p>\n\n\n\n
Consider this syntax:<\/p>\n\n\n\n
f"This is a string."<\/pre><\/div>\n\n\n\n
We have just defined a formatted string literal. We can add values to the string using curly brackets: {}.<\/p>\n\n\n\n
Some people refer to string formatting as string interpolation. These two concepts refer to the same idea: adding a value into another string.<\/p>\n\n\n\n
Let’s take a look at an example of an f string in action.<\/p>\n\n\n\n
f String Python Example<\/h2>\n\n\n\n
Suppose we want to add the name \u201cLindsay Ballantyne\u201d to a string. We could do so using this code:<\/p>\n\n\n\n
name = "Lindsay Ballantyne"\nprint(f"Your name is {name}.")<\/pre><\/div>\n\n\n\n
Our code returns:<\/p>\n\n\n\n
Your name is Lindsay Ballantyne.<\/pre><\/div>\n\n\n\n
In our code, we declare a variable called \u201cname\u201d which stores the name of our user. Then, we use an f string to add the value \u201cLindsay Ballantyne\u201d into a string.\n\n<\/p>\n\n\n\n
This shows that you can directly insert the value of a variable into an f string. The syntax is easier than all of the other formatting options, such as the format() method or a % string.\n\n<\/p>\n\n\n\n
That\u2019s not all. f strings can also support functions or any other expression, evaluated inside the string. Suppose we wanted to perform a Python mathematical function<\/a> in an f string. We could do so using this code:<\/p>\n\n\n\n
name = "Lindsay Ballantyne"\nprint(f"Your name is {name}. On your next birthday, you will be {22 + 1}.")<\/pre><\/div>\n\n\n\n
Our code returns: <\/p>\n\n\n\n
Your name is Lindsay Ballantyne. On your next birthday, you will be 23.<\/pre><\/div>\n\n\n\n
We were able to perform a mathematical function.<\/p>\n\n\n\n
This is because expressions in string literals are evaluated at run-time, and they are part of the main program. Our mathematical function was \u201c22 + 1\u201d, which we performed by enclosing the function within curly brackets.\n\n<\/p>\n\n\n\n
Multiline Python f Strings<\/h2>\n\n\n\n
The f string syntax supports multiline string formatting. You can create a multiline Python f string by enclosing multiple f strings in curly brackets.<\/p>\n\n\n\n
Suppose we wanted to format values in a multiline string. We could do so using this code:<\/p>\n\n\n\n
name = "Lindsay Ballantyne"\nemail = "lindsay.ballantyne@gmail.com"\nage = 22\n\nprofile = (\n\tf"Name: {name} \\n"\n\tf"Email: {email} \\n"\n\tf"Age: {age} \\n"\n)\n\nprint(profile)<\/pre><\/div>\n\n\n\n
Our code returns:<\/p>\n\n\n\n
Name: Lindsay Ballantyne\nEmail: lindsay.ballantyne@gmail.com\nAge: 22<\/pre><\/div>\n\n\n\n
In our code, we declared three variables \u2014 name, email, and age \u2014 which store information about our user. Then, we created a multiline string which is formatted using those variables.\n\n<\/p>\n\n\n\n
Notice how, in our code, we placed an f before each line in our multiline string. This is because, if you don\u2019t place an f in front of each line, the f string syntax will not be used.\n\n<\/p>\n\n\n\n
f String Special Characters<\/h2>\n\n\n\n
There\u2019s still one thing you need to learn before you start using f strings in your code. You need to know how to handle special characters with f strings.\n\n<\/p>\n\n\n\n
Here are a few rules you should keep in mind as you use f strings.\n\n<\/p>\n\n\n\n
Quotation Marks<\/h3>\n\n\n\n
When you\u2019re using f strings, you can use quotation marks in your expressions. But, you need to use a different type of quotation mark than you are using outside your f string. Here\u2019s an example of quotation marks being used in an f string:<\/p>\n\n\n\n
print(f"{'It is Thursday!'}")<\/pre><\/div>\n\n\n\n
Our code returns:<\/p>\n\n\n\n
It is Thursday<\/pre><\/div>\n\n\n\n
Notice that we used single quotes (\u2018) inside our f string (which is denoted using curly braces), and double quotes (\u201c\u201d) to represent our full string.<\/p>\n\n\n\n
Dictionaries<\/h3>\n\n\n\n
To reference a value in a Python dictionary<\/a>, you\u2019ll need to use quotation marks. You should make sure that you use a different kind of quotation mark when you reference each value in your dictionary.\n\n<\/p>\n\n\n\n
Here\u2019s an example of working with a dictionary and an f string:<\/p>\n\n\n\n
user = {name: "Lindsay Ballantyne", email: "lindsay.ballantyne@gmail.com"}\nprint(f{"Hello, {user['name']}. Your email address is: {user['email']}.")<\/pre><\/div>\n\n\n\n
Our code returns: <\/p>\n\n\n\n
Hello, Lindsay Ballantyne. Your email address is: lindsay.ballantyne@gmail.com<\/pre><\/div>\n\n\n\n
Note that, when we\u2019re referring to values in our dictionary, we use single quotes (\u2018\u2019). Our main f string uses double quotes (\u201c\u201d). This prevents any string formatting errors from arising in our code.\n\n<\/p>\n\n\n\n
Curly Braces<\/h3>\n\n\n\n
To use a curly brace in an f string, you need to use double braces. Here\u2019s an example of curly braces in an f string:<\/p>\n\n\n\n
print(f"{{This is a test}}")<\/pre><\/div>\n\n\n\n
Our code returns:<\/p>\n\n\n\n
{This is a test}<\/pre><\/div>\n\n\n\n
You can see that only one set of braces appeared in our end result. This is because one set of braces is used by the f string to denote that string formatting is going to take place. So, only the one set of braces inside your curly braces will appear.\n\n<\/p>\n\n\n\n
Comments<\/h3>\n\n\n\n
When you\u2019re writing an f string, your f string should not include a hashtag (#) sign. This sign denotes a comment in Python, and will cause a syntax error.\n\n<\/p>\n\n\n\n
If you want to use a hashtag in a string, make sure it is formatted in the string, instead of the f string. Here\u2019s an example of this in action:<\/p>\n\n\n\n
user_id = "202"\nprint(f"User ID: #{user_id}")<\/pre><\/div>\n\n\n\n
Our code returns: <\/p>\n\n\n\n
User ID: #202<\/pre><\/div>\n\n\n\n
We added our hashtag in before our f string curly braces. We did this to make sure that our hashtag would appear correctly in our string.<\/p>\n\n\n\n
View the Repl.it from this tutorial:<\/strong><\/p>\n\n\n\n