Python String Interpolation (original) (raw)

Last Updated : 09 Aug, 2023

**String Interpolation is the process of substituting values of variables into placeholders in a string. Let’s consider an example to understand it better, suppose you want to change the value of the string every time you print the string like you want to print “hello welcome to geeks for geeks” where the is the placeholder for the name of the user. Instead of creating a new string every time, string interpolation in Python can help you to change the placeholder with the name of the user dynamically.

Python String Interpolation

% – Formatting

% – Formatting is a feature provided by Python that can be accessed with a % operator. This is similar to the printf style function in C.

**Example: Formatting string using the % operator

Python3

n1 = 'Hello'

n2 = 'GeeksforGeeks'

print ( "Welcome to % s" % n2)

print ( "% s ! This is % s." % (n1, n2))

Output

Welcome to GeeksforGeeks Hello ! This is GeeksforGeeks.

Let’s say it’s just a complicated version. Still, we can use it if we have a lot of variables to get substituted in the string as we don’t always want to use(“string” + variable + “string” + variable + variable + “string”) this representation. So for this purpose, we can go with %-formatting.

**Note: To know more about %-formatting, refer to String Formatting in Python using %

Str.format()

str.format() works by putting in one or more replacement fields and placeholders defined by a pair of curly braces { } into a string. The value we wish to put into the placeholders and concatenate with the string passed as parameters into the format function.

**Example: Formatting strings using the format() method.

Python3

n1 = 'Hello'

n2 = 'GeeksforGeeks'

print ( '{}, {}' . format (n1, n2))

Output

Hello, GeeksforGeeks

We can also use the variable name inside the curly braces {}. This will allow us to use the parameters of format functions in any order we want.

**Example: Format functions with variables inside curly braces.

Python3

n1 = "Hello"

n2 = "GeeksForGeeks"

print ( "{b1}! This is {b2}." . format (b1 = n1, b2 = n2))

print ( "{b2}! This is {b1}." . format (b1 = n1, b2 = n2))

Output

Hello! This is GeeksForGeeks. GeeksForGeeks! This is Hello.

**Note: To know more about str.format(), refer to format() function in Python

f-strings

PEP 498 introduced a new string formatting mechanism known as Literal String Interpolation or more commonly as F-strings (because of the leading f character preceding the string literal). The idea behind f-strings is to make string interpolation simpler.

To create an f-string, prefix the string with the letter “ f ”. The string itself can be formatted in much the same way that you would with str. format(). F-strings provide a concise and convenient way to embed Python expressions inside string literals for formatting.

**Example: Formatting Strings using f-strings

Python3

n1 = 'Hello'

n2 = 'GeeksforGeeks'

print (f "{n1}! This is {n2}" )

Output

Hello! This is GeeksforGeeks (2 * 3)-10 = -4

We can also use f-strings to calculate some arithmetic operations and it will perform the inline arithmetic. See the below example –

**Example: Inline arithmetic using f-strings

Python3

a = 2

b = 3

c = 10

print (f "({a} * {b})-{c} = {(2 * 3)-10}" )

**Note: To know more about f-strings, refer to f-strings in Python

String Template Class

In the String module, Template Class allows us to create simplified syntax for output specification. The format uses placeholder names formed by $ with valid Python identifiers (alphanumeric characters and underscores). Surrounding the placeholder with braces allows it to be followed by more alphanumeric letters with no intervening spaces. Writing creates a single escaped $:

**Example: Formatting string using Template Class

Python3

from string import Template

n1 = 'Hello'

n2 = 'GeeksforGeeks'

n = Template( '$n3 ! This is $n4.' )

print (n.substitute(n3 = n1, n4 = n2))

Output

Hello ! This is GeeksforGeeks.

**Note: To know more about the String Template class, refer to String Template Class in Python