fstrings in Python (original) (raw)

f-strings in Python

Last Updated : 19 Jun, 2024

Python offers a powerful feature called **f-strings (formatted string literals) to simplify string formatting and interpolation. **f-strings is introduced in Python 3.6 it provides a concise and intuitive way to embed expressions and variables directly into strings. The idea behind f-strings is to make string interpolation simpler.

How to use f-strings in Python

To create an f-string, prefix the string with the letter “ **f ”. The string itself can be formatted in much the same way that you would with str.format(). F-strings provide a concise and convenient way to embed Python expressions inside string literals for formatting.

In the below example, we have used the f-string inside a print() method to print a string. We use curly braces to use a variable value inside f-strings, so we define a variable ‘val’ with ‘Geeks’ and use this inside as seen in the code below **‘val’ with **‘Geeks’. Similarly, we use the ‘name’ and **the variable inside a second print statement.

Python `

Python3 program introducing f-string

val = 'Geeks' print(f"{val}for{val} is a portal for {val}.")

name = 'Om' age = 22 print(f"Hello, My name is {name} and I'm {age} years old.")

`

**Output

GeeksforGeeks is a portal for Geeks.
Hello, My name is Om and I'm 22 years old.

In this example, we have printed today’s date using the **datetime module in Python with **f-string. For that firstly, we import the datetime module after that we print the date using f-sting. Inside f-string **‘today’ assigned the current date and ****%B**, ****%d**, and ****%Y** represents the **full month, **day of month, and **year respectively.

Python `

Prints today's date with help

of datetime library

import datetime

today = datetime.datetime.today() print(f"{today:%B %d, %Y}")

`

**Output

May 23, 2024

**Note: F-strings are faster than the two most commonly used string formatting mechanisms, which are % formatting and str.format().

Quotation Marks in f-string in Python

To use any type of quotation marks with the f-string in Python we have to make sure that the quotation marks used inside the expression are not the same as quotation marks used with the f-string.

Python `

print(f"'GeeksforGeeks'")

print(f"""Geeks"for"Geeks""")

print(f'''Geeks'for'Geeks''')

`

**Output

'GeeksforGeeks'
Geeks"for"Geeks
Geeks'for'Geeks

Evaluate Expressions with f-Strings in Python

We can also evaluate expressions with f-strings in Python. To do so we have to write the expression inside the curly braces in f-string and the evaluated result will be printed as shown in the below code’s output.

Python `

english = 78 maths = 56 hindi = 85

print(f"Ram got total marks {english + maths + hindi} out of 300")

`

**Output

Ram got total marks 219 out of 300

Errors while using f-string in Python

Backslashes in f-string in Python

In Python f-string, Backslash Cannot be used in format string directly.

Python `

f"newline: {ord('\n')"

`

**Output

Hangup (SIGHUP)
File "Solution.py", line 1
f"newline: {ord('\n')"
^
SyntaxError: f-string expression part cannot include a backslash

However, we can put the backslash into a variable as a workaround though :

Python `

newline = ord('\n')

print(f"newline: {newline}")

`

**Output

newline: 10

Inline comments in f-string in Python

We cannot use comments inside F-string expressions. It will give an error:

Python `

f"GeeksforGeeks is {5*2 + 3 #geeks-5} characters."

`

**Output:

Hangup (SIGHUP)
File "Solution.py", line 1
f"GeeksforGeeks is {5*2 + 3 #geeks-5} characters."
^
SyntaxError: f-string expression part cannot include '#'

Printing Braces using f-string in Python

If we want to show curly braces in the f-string’s output then we have to use double curly braces in the f-string. Note that for each single pair of braces, we need to type double braces as seen in the below code.

Python `

Printing single braces

print(f"{{Hello, Geek}}")

Printing double braces

print(f"{{{{Hello, Geek}}}}")

`

**Output

{Hello, Geek}
{{Hello, Geek}}

Printing Dictionaries key-value using f-string in Python

While working with dictionaries, we have to make sure that if we are using double quotes (“) with the f-string then we have to use single quote (‘) for keys inside the f-string in Python and vice-versa. Otherwise, it will throw a syntax error.

Python `

Geek = { 'Id': 112, 'Name': 'Harsh'}

print(f"Id of {Geek["Name"]} is {Geek["Id"]}")

`

**Output

Hangup (SIGHUP)
File "Solution.py", line 4
print(f"Id of {Geek["Name"]} is {Geek["Id"]}")
^
SyntaxError: invalid syntax

Using the same type of quotes for f-string and key

Python `

Geek = { 'Id': 100, 'Name': 'Om'}

print(f"Id of {Geek['Name']} is {Geek['Id']}")

`

**Output

Id of Om is 100