2.5 KiB
2.5 KiB
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| Python f-strings |
f-strings in Python
In Python version 3.6, a new method of formatting strings was implemented. The new method is called Literal string interpolation (though commonly referred to as an f-string, due to f prefix at the beginning of the string).
The use of f-string allows the programmer to dynamically insert a variable into a string in a clean and concise manner. In addition to inserting variables into a string this feature also provides the ability for a programmer to evaluate expressions, join the contents of collection, and even invoke functions within the f-string.
To perform these dynamic behaviours within an f-string we wrap them inside curly brackets within the string, and prepend a lower case f to the beginning of the string (before the opening quote).
Examples
Dynamically inserting a variable into a string at runtime:
Input
name = 'Jon Snow'
greeting = f'Hello! {name}.'
print(greeting)
Output
Hello! Jon Snow.
Multiple variables, of different types, can be inserted in the same string:
Input
item_id = 'P12305'
price = 425.50
print(f'Item {item_id} costs {price} USD.')
Output
Item P12305 costs 425.50 USD.
Evaluate an expression in a string:
Input
val1 = 2
val2 = 3
expr = f'The sum of {val1} + {val2} is {val1 + val2}'
print(expr)
Output
The sum of 2 + 3 is 5
Calling a function and inserting output within a string:
Input
def sum(*args):
result = 0
for arg in args:
result += arg
return result
func = f'The sum of 3 + 5 is {sum(3, 5)}'
print(func)
Output
The sum of 3 + 5 is 8
Joining the contents of a collection within a string:
Input
fruits = ['Apple', 'Banana', 'Pear']
list_str = f'List of fruits: {", ".join(fruits)}'
print(list_str)
Output
List of fruits: Apple, Banana, Pear
Convert an integer to 8-bit binary
Input
num = 42
print(f'The binary of {num} is {num:08b}')
Output
The binary of 42 is 00101010
Using Object with f-strings
Input
class Book:
def __init__(self, title, author):
self.title = title
self.author = author
def __str__(self):
return f"{self.title} by {self.author}"
book = Book("A Clash of Kings", "George R. R. Martin")
print(f"{book}")
Output
A Clash of Kings by George R. R. Martin