Formatted String Literals (F-Strings) in Python

Python now provides new way to format strings, called f-strings. This features is available from Python 3.6 under PEP-498. They are so called (f-string) because of the letter ‘f’ prefix with a string. The letter ‘f’ also indicates that these f-strings can be used for formatting.

Below are some of the examples to demonstrates the use of f-strings.

Program#1

name = 'Rajesh'
age = 13 * 3
fString = f'My name is {name} and my age is {age}'
print(fString)
#We can use Uppercase 'F' instead of lowercase 'f'.
print(F'My name is {name} and my age is {age}')
#As the fString valuation is done, giving another value to the variable will not change fstring value.
name = 'Zack'
age = 44
print(fString)

Output

My name is Rajesh and my age is 39
My name is Rajesh and my age is 39
My name is Rajesh and my age is 39

Example#2 – f-strings with expressions and conversions

from datetime import datetime

name = 'Rajesh'
age = 13 * 3
dt = datetime.now()
print(f' Age after ten years will be {age + 10}')
print(f'Name with quotes = {name!r}')
print(f'Default formatted Date = {dt}')
print(f'Modified Date format = {dt: %d/%m/%Y}')

Output

Age after ten years will be 49
Name with quotes = 'Rajesh'
Default formatted Date = 2019-02-11 14:52:05.307841
Modified Date format = 11/02/2019

Example#3: Objects and attributes

class Vehicle:
   Model = 0
   Brand = ''
def __init__(self, Model, Brand):
   self.Model = Model
   self.Brand = Brand
def __str__(self):
   return f'E[Model={self.Model}, Brand = {self.Brand}]'
Car = Vehicle (2018, 'Maruti')
print(Car)
print(f'Vehicle: {Car}\nModel is {Car.Model} and Brand is {Car.Brand}')

Output

E[Model=2018, Brand = Maruti]
Vehicle: E[Model=2018, Brand = Maruti]
Model is 2018 and Brand is Maruti

Example#4: calling functions

We can call functions in f-strings formatting too.

def Multiply(x,y):
   return x*y
print( f'Multiply(40,20) = {Multiply(40,20)}')

Output

Multiply(40,20) = 800

Example# 5: Lambda expressions

x = -40.9
print(f' Lambda absolute of (-40.9) is : {(lambda x: abs(x)) (x)}')
print(f' Lambda Square of 2^4 is: {(lambda x: pow(x, 2)) (4)}')

Output

Lambda absolute of (-40.9) is : 40.9
Lambda Square of 24 is: 16