Python Tutorials · Python String Formatting

Python String Formatting

Learn all about Python String Formatting in this comprehensive tutorial.

5 min read intermediate

Python Try...Except

Python None

•F-String was introduced in Python 3.
•F-string allows you to format selected parts of a string.
•To format values in an f-string, add placeholders {}, a placeholder can contain variables, operations, functions, and modifiers to format the value.
•You can perform Python operations inside the placeholders.
•You can execute functions inside the placeholder:
•At the beginning of this chapter we explained how to use the .
•Before Python 3.
•If you want to use more values, just add more values to the format() method:
•You can use index numbers (a number inside the curly brackets {0}) to be sure the values are placed in the correct placeholders:
•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.

Introduction

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:

python

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.

python

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:

python

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:

python

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:

python

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

print(txt)

You can perform math operations on variables:

python

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:

python

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:

python

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:

python

def myconverter(val_1):
  return val_1 * 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:

python

price = 59000

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

print(txt)

Here is a list of all the formatting types.

Formatting Types
:<	Try it	Left aligns the result (within the available space)
:>	Try it	Right aligns the result (within the available space)
:^	Try it	Center aligns the result (within the available space)
:=	Try it	Places the sign to the left most position
:+	Try it	Use a plus sign to indicate if the result is positive or negative
:-	Try it	Use a minus sign for negative values only
:	Try it	Use a space to insert an extra space before positive numbers (and a minus sign before negative numbers)
:,	Try it	Use a comma as a thousand separator
:_	Try it	Use a underscore as a thousand separator
:b	Try it	Binary format
:c		Converts the value into the corresponding Unicode character
:d	Try it	Decimal format
:e	Try it	Scientific format, with a lower case e
:E	Try it	Scientific format, with an upper case E
:f	Try it	Fix point number format
:F	Try it	Fix point number format, in uppercase format (show inf and nan as INF and NAN)
:g		General format
:G		General format (using a upper case E for scientific notations)
:o	Try it	Octal format
:x	Try it	Hex format, lower case
:X	Try it	Hex format, upper case
:n		Number format
:%	Try it	Percentage format

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:

python

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

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

python

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:

python

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

And add more placeholders:

python

quantity = 3itemno = 567price = 49myorder = "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:

python

quantity = 3itemno = 567price = 49myorder = "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:

python

age = 36name = "Alice"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"):

python

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

Module quiz

2 questions

Which of the following is true about Python String Formatting?

It is strictly typedIt is evaluated at runtimeIt requires explicit memory managementIt is deprecated

What is the most common pitfall when working with Python String Formatting?

SyntaxErrorIndentationErrorNameErrorTypeError

Answer all questions to submit.

Python Try...Except

Python None

Python String Formatting

AI Summary

Introduction

F-Strings

Placeholders and Modifiers

Perform Operations in F-Strings

Execute Functions in F-Strings

More Modifiers

String format()

Multiple Values

Index Numbers

Named Indexes

Module quiz