Python - f-strings

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With the version 3.6, Python introduced a new string formatting method, f-strings or Literal String Interpolation. With this formatting method you can use embedded Python expressions inside string constants. Python f-strings are a faster, more readable, more concise, and less error prone.

Print Variables Using f-string

To print variables using f-strings, you can simply put them inside the placeholders ({}). The string starts with a 'f' prefix, and one or more place holders are inserted in it, whose value is filled dynamically.

Example

In the below example, we are printing the variables using f-strings.

name = 'Rajesh'
age = 23
fstring = f'My name is {name} and I am {age} years old'
print (fstring)

It will produce the following output −

My name is Rajesh and I am 23 years old

Evaluate Expressions Using f-Strings

The f-string can also be used to evaluate expressions inside the {} placeholder.

Example

The following example shows how to evaluate expression using f-strings.

price = 10
quantity = 3
fstring = f'Price: {price} Quantity : {quantity} Total : {price*quantity}'
print (fstring)

It will produce the following output −

Price: 10 Quantity : 3 Total : 30

Printing Dictionaries Key-Value Using f-string

The placeholders can be populated by dictionary values. Dictionary is one of the built-in data types in Python that stores unordered collection of key-value pairs.

Example

In the following example, we are formatting a dictionary using f-strings.

user = {'name': 'Ramesh', 'age': 23}
fstring = f"My name is {user['name']} and I am {user['age']} years old"
print (fstring)

It will produce the following output −

My name is Ramesh and I am 23 years old

Self Debugging Expression in f-string

The = character is used for self debugging the expression in f-string as shown in the following example −

price = 10
quantity = 3
fstring = f"Total : {price*quantity=}"
print (fstring)

It will produce the following output −

Total : price*quantity=30

Call User-Defined Function Using f-string

It is also possible to call a user defined function inside the f-string expression. To do so, simply use the function name by passing required parameters.

Example

The below example shows how to call a method inside f-string.

def total(price, quantity):
   return price*quantity

price = 10
quantity = 3

fstring = f'Price: {price} Quantity : {quantity} Total : {total(price, quantity)}'
print (fstring)

It will produce the following output −

Price: 10 Quantity : 3 Total : 30

Precision Handling Using f-string

Python f-strings also support formatting floats with precision specifications, as done by format() method and string formatting operator %.

name="Rajesh"
age=23
percent=55.50

fstring = f"My name is {name} and I am {age} years old and I have scored {percent:6.3f} percent marks"
print (fstring)

It will produce the following output −

My name is Rajesh and I am 23 years old and I have scored 55.500 percent marks

String Alignment Using f-string

For string variable, you can specify the alignment just as we did with format() method and formatting operator %.

name='TutorialsPoint'
fstring = f'Welcome To {name:>20} The largest Tutorials Library'
print (fstring)

fstring = f'Welcome To {name:<20} The largest Tutorials Library'
print (fstring)

fstring = f'Welcome To {name:^20} The largest Tutorials Library'
print (fstring)

It will produce the following output −

Welcome To       TutorialsPoint The largest Tutorials Library
Welcome To TutorialsPoint       The largest Tutorials Library
Welcome To    TutorialsPoint    The largest Tutorials Library

Print Numbers in Other Formats Using f-string

The f-strings can display numbers with hexadecimal, octal and scientific notation when used with "x", "o" and "e" respectively.

Example

The below example shows how to format numbers using f-string.

num= 20
fstring = f'Hexadecimal : {num:x}'
print (fstring)

fstring = f'Octal :{num:o}'
print (fstring)

fstring = f'Scientific notation : {num:e}'
print (fstring)

It will produce the following output −

Hexadecimal : 14
Octal :24
Scientific notation : 2.000000e+01