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:
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
Add a placeholder for the price variable:
price = 59
txt = f"The price is {price} dollars"
print(txt)
Try it Yourself »
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
Display the price with 2 decimals:
price = 59
txt = f"The price is {price:.2f} dollars"
print(txt)
Try it Yourself »
You can also format a value directly without keeping it in a variable:
Example
Display the value 95 with 2 decimals:
txt = f"The price is {95:.2f} dollars"
print(txt)
Try it Yourself »
Perform Operations in F-Strings
You can perform Python operations inside the placeholders.
You can do math operations:
Example
Perform a math operation in the placeholder, and return the result:
txt = f"The price is {20 * 59} dollars"
print(txt)
Try it Yourself »
You can perform math operations on variables:
Example
Add taxes before displaying the price:
price = 59
tax = 0.25
txt = f"The price is {price + (price * tax)} dollars"
print(txt)
Try it Yourself »
You can perform if...else statements inside the placeholders:
Example
Return "Expensive" if the price is over 50, otherwise return "Cheap":
price = 49
txt = f"It is very {'Expensive' if price>50 else 'Cheap'}"
print(txt)
Try it Yourself »
Execute Functions in F-Strings
You can execute functions inside the placeholder:
Example
Use the string method upper()to convert a
value into upper case letters:
fruit = "apples"
txt = f"I love {fruit.upper()}"
print(txt)
Try it Yourself »
The function does not have to be a built-in Python method, you can create your own functions and use them:
Example
Create a function that converts feet into meters:
def myconverter(x):
return x * 0.3048
txt = f"The plane is flying at a {myconverter(30000)} meter altitude"
print(txt)
Try it Yourself »
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
Use a comma as a thousand separator:
price = 59000
txt = f"The price is {price:,} dollars"
print(txt)
Try it Yourself »
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:
Example
Add a placeholder where you want to display the price:
price = 49
txt = "The price is {} dollars"
print(txt.format(price))
Try it Yourself »
You can add parameters inside the curly brackets to specify how to convert the value:
Example
Format the price to be displayed as a number with two decimals:
txt = "The price is {:.2f} dollars"
Try it Yourself »
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))
Try it Yourself »
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))
Try it Yourself »
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))
Try it Yourself »
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"))
Try it Yourself »
