Python String Formatting – How to format String?

String formatting allows you to create dynamic strings by combining variables and values. In this article, we will discuss about 5 ways to format a string.

You will learn different methods of string formatting with examples for better understanding. Let’s look at them now!

How to Format Strings in Python

There are five different ways to perform string formatting in Python

• Formatting with % Operator.
• Formatting with format() string method.
• Formatting with string literals, called f-strings.
• Formatting with String Template Class
• Formatting with center() string method.

So we will see the entirety of the above-mentioned ways, and we will also focus on which string formatting strategy is the best.

1. How to Format String using % Operator

It is the oldest method of string formatting. Here we use the modulo % operator. The modulo % is also known as the “string-formatting operator”.

Python Format String Using the % Operator

In the expression “The mangy, scrawny stray dog %s gobbled down” % ‘hurriedly’, the %s placeholder within the string is replaced by the value ‘hurriedly’.

Python3

print("The mangy, scrawny stray dog %s gobbled down" %'hurriedly' +
      "the grain-free, organic dog food.")

Output

The mangy, scrawny stray dog hurriedly gobbled downthe grain-free, organic dog food.

Injecting Multiple Strings using the modulo Operator

Here we are inserting multiple strings with the % operator.

Python3

x = 'looked'

print("Misha %s and %s around"%('walked',x))

Output

Misha walked and looked around

Precision Handling in Python using % operator

Floating-point numbers use the format %a.bf. Here, a would be the minimum number of digits to be present in the string; these might be padded with white space if the whole number doesn’t have this many digits.

Close to this, bf represents how many digits are to be displayed after the decimal point. 

In this code, the string ‘The value of pi is: %5.4f’ contains a format specifier %5.4f. The %5.4f format specifier is used to format a floating-point number with a minimum width of 5 and a precision of 4 decimal places.

Python3

print('The value of pi is: %5.4f' %(3.141592))

Output

The value of pi is: 3.1416

Multiple format conversion types

In the given code, the formatting string Python is converted to Integer and floating point with %d,%f.

Python3

variable = 12
string = "Variable as integer = %d \n\
Variable as float = %f" %(variable, variable)
print (string)

Output

Variable as integer = 12 
Variable as float = 12.000000

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

2. How to Format String using format() Method

Format() method was introduced with Python3 for handling complex string formatting more efficiently.

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

Syntax: ‘String here {} then also {}’.format(‘something1′,’something2’)

Formatting String Python using format() Method

This code is using {} as a placeholder and then we have called.format() method on the ‘equal’ to the placeholder.

Python3

print('We all are {}.'.format('equal'))

Output

We all are equal.

Index-based Insertion

In this code, curly braces {} with indices are used within the string ‘{2} {1} {0}’ to indicate the positions where the corresponding values will be placed.

Python3

print('{2} {1} {0}'.format('directions',
                           'the', 'Read'))

Output

Read the directions

Insert object by Assigning Keywords

In this code, curly braces {} with named placeholders ({a}, {b}, {c}) are used within the string ‘a: {a}, b: {b}, c: {c}’ to indicate the positions where the corresponding named arguments will be placed.

Python3

print('a: {a}, b: {b}, c: {c}'.format(a = 1,
                                      b = 'Two',
                                      c = 12.3))

Output

a: 1, b: Two, c: 12.3

Reuse the inserted objects

In this code, curly braces {} with named placeholders ({p}) are used within the string ‘The first {p} was alright, but the {p} {p} was tough.’ to indicate the positions where the corresponding named argument p will be placed.

Python3

print(
    'The first {p} was alright, but the {p} {p} was tough.'.format(p='second'))

Output

The first second was alright, but the second second was tough.

Float Precision with the.format() Method

Syntax: {[index]:[width][.precision][type]}

The type can be used with format codes:

• ‘d’ for integers
• ‘f’ for floating-point numbers
• ‘b’ for binary numbers
• ‘o’ for octal numbers
• ‘x’ for octal hexadecimal numbers
• ‘s’ for string
• ‘e’ for floating-point in an exponent format

Example:

Both the codes are doing string formatting. The first String is formatted with ‘%’ and the second String is formatted with .format().

Python3

print('The valueof pi is: %1.5f' %3.141592)
print('The valueof pi is: {0:1.5f}'.format(3.141592))

Output

The valueof pi is: 3.14159
The valueof pi is: 3.14159

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

3. Understanding Python f-string

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-String in Python is to make string interpolation simpler.

To create an f-string in Python, 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.

String Formatting with F-Strings

In this code, the f-string f”My name is {name}.” is used to interpolate the value of the name variable into the string.

Python3

name = 'Ele'
print(f"My name is {name}.")

Output

My name is Ele.

This new formatting syntax is very powerful and easy. You can also insert arbitrary Python expressions and you can even do arithmetic operations in it.

Arithmetic operations using F-strings

In this code, the f-string f” He said his age is {2 * (a + b)}.” is used to interpolate the result of the expression 2 * (a + b) into the string.

Python3

a = 5
b = 10
print(f"He said his age is {2 * (a + b)}.")

Output

He said his age is 30.

We can also use lambda expressions in f-string formatting.

Lambda Expressions using F-strings

In this code, an anonymous lambda function is defined using lambda x: x*2. This lambda function takes an argument x and returns its double.

Python3

print(f"He said his age is {(lambda x: x*2)(3)}")

Output

He said his age is 6

Float precision in the f-String Method

In this code, f-string formatting is used to interpolate the value of the num variable into the string.

Syntax: {value:{width}.{precision}}

Python3

num = 3.14159

print(f"The valueof pi is: {num:{1}.{5}}")

Output

The valueof pi is: 3.1416

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

4. 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 $:

Formatting String Python Using Template Class

This code imports the Template class from the string module. The Template class allows us to create a template string with placeholders that can be substituted with actual values. Here we are substituting the values n1 and n2 in place of n3 and n4 in the string n.

Python3

from string import Template

n1 = 'Hello'
n2 = 'GeeksforGeeks'

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

# and pass the parameters into the
# template string.
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

5. How to Format String using center() Method

The center() method is a built-in method in Python’s str class that returns a new string that is centered within a string of a specified width. 

Formatting string using center() method

This code returns a new string padded with spaces on the left and right sides.

Python3

string = "GeeksForGeeks!"
width = 30

centered_string = string.center(width)

print(centered_string)

Output

        GeeksForGeeks!        

Python Format String: % vs. .format vs. f-string literal

f-strings are faster and better than both %-formatting and str.format(). f-strings expressions are evaluated at runtime, and we can also embed expressions inside f-string, using a very simple and easy syntax.

The expressions inside the braces are evaluated in runtime and then put together with the string part of the f-string and then the final string is returned.

Note: Use Template String if the string is a user-supplied string Else  Use f-Strings if you are on Python 3.6+, and. format() method if you are not.

We have covered all 5 ways of string formatting in Python. There are many use cases and examples for each method. We also compared these methods to find which one is most efficient to use in real-life projects.