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.
Print Variables using f-string in Python
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.
Print date using f-string in Python
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
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
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