Python String Formatting with F-Strings

Discover the modern way to format strings in Python using F-Strings, introduced in Python 3.6. Learn how F-Strings simplify string formatting by placing an f in front of the string literal. Compare this with the older format() method used before Python 3.6.

Python String Formatting

F-Strings, introduced in Python 3.6, are now the preferred method for formatting strings. Before Python 3.6, the format() method was used.

F-Strings

F-Strings allow you to format specific parts of a string by placing an f in front of the string literal:

txt = f"The price is 49 dollars"
print(txt)

The price is 49 dollars

Placeholders and Modifiers

F-Strings use placeholders ({}) to include variables, operations, functions, and modifiers within the string:

price = 59
txt = f"The price is {price} dollars"
print(txt)

The price is 59 dollars

Modifiers can format values by adding a colon (:) followed by a formatting type, like .2f for fixed-point numbers with two decimals:

price = 59
txt = f"The price is {price:.2f} dollars"
print(txt)

The price is 59.00 dollars

You can format values directly within the f-string:

txt = f"The price is {95:.2f} dollars"
print(txt)

The price is 95.00 dollars

Perform Operations in F-Strings

F-Strings allow you to perform operations inside placeholders, such as math operations:

txt = f"The price is {20 * 59} dollars"
print(txt)

The price is 1180 dollars

Or perform operations on variables:

price = 59
tax = 0.25
txt = f"The price is {price + (price * tax)} dollars"
print(txt)

The price is 73.75 dollars

You can also use if...else statements inside placeholders:

price = 49
txt = f"It is very {'Expensive' if price > 50 else 'Cheap'}"
print(txt)

It is very Cheap

Execute Functions in F-Strings

Functions can be executed inside placeholders:

fruit = "apples"
txt = f"I love {fruit.upper()}"
print(txt)

I love APPLES

You can also use user-defined functions:

def myconverter(x):
    return x * 0.3048

txt = f"The plane is flying at a {myconverter(30000)} meter altitude"
print(txt)

The plane is flying at a 9144.0 meter altitude

More Modifiers

There are several other modifiers for formatting values, such as using a comma as a thousand separator:

price = 59000
txt = f"The price is {price:,} dollars"
print(txt)

The price is 59,000 dollars

Here is a list of all the formatting types:

String format()

Before Python 3.6, the format() method was used for string formatting. It is still available but less preferred due to the efficiency and readability of f-strings. The format() method also uses curly brackets as placeholders, with slightly different syntax:

price = 499
txt = "The price is {} dollars"
print(txt.format(price))

The price is 499 dollars

You can add parameters inside the curly brackets to specify formatting:

txt = "The price is {:.2f} dollars"

If you want to use multiple values, add more values to the format() method and placeholders:

quantity = 30
itemno = 867
price = 99
myorder = "I want {} pieces of item number {} for {:.2f} dollars."
print(myorder.format(quantity, itemno, price))

I want 30 pieces of item number 867 for 99.00 dollars.

Using index numbers ensures values are placed correctly:

quantity = 30
itemno = 895
price = 94
myorder = "I want {0} pieces of item number {1} for {2:.2f} dollars."
print(myorder.format(quantity, itemno, price))

I want 30 pieces of item number 895 for 94.00 dollars.

You can refer to the same value more than once by using index numbers:

age = 50
name = "Alan"
txt = "His name is {1}. {1} is {0} years old."
print(txt.format(age, name))

His name is Alan. Alan is 50 years old.

Named indexes can also be used by entering a name inside the curly brackets:

myorder = "I have a {carname}, it is a {model}."
print(myorder.format(carname = "Tata", model = "Safari"))

I have a Tata, it is a Safari.