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 <name> welcome to geeks for geeks" where the <name> is the placeholder for the name of the user. Instead of creating a new string every time, string interpolation inPythoncan 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

n1='Hello'n2='GeeksforGeeks'# for single substitutionprint("Welcome to% s"%n2)# for single and multiple substitutions()# mandatoryprint("% s ! This is% s."%(n1,n2))

Welcome to GeeksforGeeksHello ! 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 toString 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.

n1='Hello'n2='GeeksforGeeks'# for single substitutionprint('{},{}'.format(n1,n2))

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.

n1="Hello"n2="GeeksForGeeks"# for single or multiple substitutions# let's say b1 and b2 are formal parameters# and n1 and n2 are actual parametersprint("{b1}! This is{b2}.".format(b1=n1,b2=n2))# we can also change the order of the# variables in the string without changing# the parameters of format functionprint("{b2}! This is{b1}.".format(b1=n1,b2=n2))

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

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

f-strings

PEP 498 introduced a new string formatting mechanism known as Literal String Interpolation or more commonly asF-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

n1='Hello'n2='GeeksforGeeks'# f tells Python to restore the value of two# string variable name and program inside braces {}print(f"{n1}! This is{n2}")

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

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

(2 * 3)-10 = -4

Note: To know more about f-strings, refer tof-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

fromstringimportTemplaten1='Hello'n2='GeeksforGeeks'# made a template which we used to# pass two variable so n3 and n4# formal and n1 and n2 actualn=Template('$n3 ! This is $n4.')# and pass the parameters into the template string.print(n.substitute(n3=n1,n4=n2))

Hello ! This is GeeksforGeeks.

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

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