Python String Formatting

F-String was introduced in Python 3.6, and is now the preferred way of formatting strings.

Before Python 3.6 we had to use the format() method.

F-Strings

F-string allows you to format selected parts of a string.

To specify a string as an f-string, simply put an f in front of the string literal, like this:

Example

txt = f"The price is 49 dollars"

print(txt)

Placeholders and Modifiers

To format values in an f-string, add placeholders {}, a placeholder can contain variables, operations, functions, and modifiers to format the value.

Example

price = 59

txt = f"The price is {price} dollars"

print(txt)

A placeholder can also include a modifier to format the value.

A modifier is included by adding a colon : followed by a legal formatting type, like .2f which means fixed point number with 2 decimals:

Example

price = 59

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

print(txt)

You can also format a value directly without keeping it in a variable:

Example

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

print(txt)

Perform Operations in F-Strings

You can perform Python operations inside the placeholders.

You can do math operations:

Example

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

print(txt)

You can perform math operations on variables:

Example

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

print(txt)

You can perform if...else statements inside the placeholders:

Example

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

print(txt)

Execute Functions in F-Strings

You can execute functions inside the placeholder:

Example

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

print(txt)

The function does not have to be a built-in Python method, you can create your own functions and use them:

Example

def myconverter(x):
  return x * 0.3048

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

print(txt)

More Modifiers

At the beginning of this chapter we explained how to use the .2f modifier to format a number into a fixed point number with 2 decimals.

There are several other modifiers that can be used to format values:

Example

price = 59000

txt = f"The price is {price:,} dollars"

print(txt)

Here is a list of all the formatting types.

String format()

Before Python 3.6 we used the format() method to format strings.

The format() method can still be used, but f-strings are faster and the preferred way to format strings.

The next examples in this page demonstrates how to format strings with the format() method.

The format() method also uses curly brackets as placeholders {}, but the syntax is slightly different:

Example

  price = 49
txt = "The price is {} dollars"
print(txt.format(price))

You can add parameters inside the curly brackets to specify how to convert the value:

Example

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

Check out all formatting types in our String format() Reference.

Multiple Values

If you want to use more values, just add more values to the format() method:

print(txt.format(price, itemno, count))

And add more placeholders:

Example

  quantity = 3
itemno = 567
price = 49
myorder = "I want {} pieces of
  item number {} for {:.2f} dollars."
print(myorder.format(quantity, itemno, price))

Index Numbers

You can use index numbers (a number inside the curly brackets {0}) to be sure the values are placed in the correct placeholders:

Example

  quantity = 3
itemno = 567
price = 49
myorder = "I want {0} pieces of
  item number {1} for {2:.2f} dollars."
print(myorder.format(quantity, itemno, price))

Also, if you want to refer to the same value more than once, use the index number:

Example

  age = 36
name = "John"
txt = "His name is {1}. {1} is {0} years old."
print(txt.format(age,
  name))

Named Indexes

You can also use named indexes by entering a name inside the curly brackets {carname}, but then you must use names when you pass the parameter values txt.format(carname = "Ford"):

Example

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