PEP-0498 Literal String Interpolation

See also

Abstract

Python supports multiple ways to format text strings.

These include %-formatting [1], str.format() [2], and string.Template [3].

Each of these methods have their advantages, but in addition have disadvantages that make them cumbersome to use in practice.

This PEP proposed to add a new string formatting mechanism: Literal String Interpolation .

In this PEP, such strings will be referred to as “f-strings”, taken from the leading character used to denote such strings, and standing for “formatted strings”.

This PEP does not propose to remove or deprecate any of the existing string formatting mechanisms.

F-strings provide a way to embed expressions inside string literals, using a minimal syntax. It should be noted that an f-string is really an expression evaluated at run time, not a constant value.

In Python source code, an f-string is a literal string, prefixed with ‘f’ , which contains expressions inside braces.

The expressions are replaced with their values. Some examples are: 

>>> import datetime
>>> name = 'Fred'
>>> age = 50
>>> anniversary = datetime.date(1991, 10, 12)
>>> f'My name is {name}, my age next year is {age+1}, my anniversary is {anniversary:%A, %B %d, %Y}.'
'My name is Fred, my age next year is 51, my anniversary is Saturday, October 12, 1991.'
>>> f'He said his name is {name!r}.'
"He said his name is 'Fred'."