136 lines
2.5 KiB
Markdown
136 lines
2.5 KiB
Markdown
---
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title: Python f-strings
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---
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# f-strings in Python
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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).
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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.
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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).
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## Examples
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### Dynamically inserting a variable into a string at runtime:
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#### Input
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```python
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name = 'Jon Snow'
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greeting = f'Hello! {name}.'
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print(greeting)
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```
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#### Output
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```
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Hello! Jon Snow.
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```
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### Multiple variables, of different types, can be inserted in the same string:
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### Input
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```python
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item_id = 'P12305'
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price = 425.50
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print(f'Item {item_id} costs {price} USD.')
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```
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#### Output
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```
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Item P12305 costs 425.50 USD.
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```
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### Evaluate an expression in a string:
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#### Input
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```python
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val1 = 2
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val2 = 3
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expr = f'The sum of {val1} + {val2} is {val1 + val2}'
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print(expr)
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```
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#### Output
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```
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The sum of 2 + 3 is 5
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```
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### Calling a function and inserting output within a string:
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#### Input
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```python
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def sum(*args):
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result = 0
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for arg in args:
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result += arg
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return result
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func = f'The sum of 3 + 5 is {sum(3, 5)}'
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print(func)
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```
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#### Output
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```
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The sum of 3 + 5 is 8
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```
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### Joining the contents of a collection within a string:
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#### Input
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```python
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fruits = ['Apple', 'Banana', 'Pear']
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list_str = f'List of fruits: {", ".join(fruits)}'
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print(list_str)
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```
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#### Output
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```
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List of fruits: Apple, Banana, Pear
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```
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### Convert an integer to 8-bit binary
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#### Input
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```python
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num = 42
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print(f'The binary of {num} is {num:08b}')
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```
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#### Output
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```
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The binary of 42 is 00101010
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```
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### Using Object with f-strings
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#### Input
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```python
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class Book:
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def __init__(self, title, author):
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self.title = title
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self.author = author
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def __str__(self):
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return f"{self.title} by {self.author}"
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book = Book("A Clash of Kings", "George R. R. Martin")
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print(f"{book}")
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```
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##### Output
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```
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A Clash of Kings by George R. R. Martin
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```
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### Sources
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https://www.python.org/dev/peps/pep-0498/
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