Use of f-string string formatting in Python

1. Basic usage

name = "Alice"
 age = 25
 
 # Embed variables using f-string message = f"My name is {name} and I am {age} years old."
 print(message)
 
 # Output My name is Alice and I am 25 years old.

2. Embed expressions

a = 5
 b = 10
 
 # Embed expressions using f-string result = f"The sum of {a} and {b} is {a + b}."
 print(result)
 
 # Output The sum of 5 and 10 is 15.

3. Format output

1. Digital formatting

1.1 Floating point number formatting

grammar:{value:.nf},innis the number of decimal places reserved.

pi = 3.141592653589793
 
 # Keep two decimal places formatted_pi = f"Pi rounded to 2 decimal places: {pi:.2f}"
 print(formatted_pi)
 
 #Output Pi rounded to 2 decimal places: 3.14

1.2 Integer Zero Complement

grammar:{value:0nd},innIt is the total number of digits, and the insufficient part is used0Fill.

number = 42
 
 # Add zero to 5 digits formatted_number = f"The number is {number:05d}"
 print(formatted_number)
 
 #Output The number is 00042

1.3 thousand separator

grammar:{value:,}, use commas to separate thousands of digits.

population = 1234567890
 
 # Add a thousand separator formatted_population = f"The world population is {population:,}"
 print(formatted_population)
 
 #Output The world population is 1,234,567,890

1.4 percent formatting

grammar:{value:.n%},innis the number of decimal places reserved.

ratio = 0.4567
 
 # Format as a percentage, retain two decimal places formatted_ratio = f"The ratio is {ratio:.2%}"
 print(formatted_ratio)
 
 #Output The ratio is 45.67%

2. String formatting

2.1 Alignment and fill

grammar:{value:width}or{value:<width}、{value:>width}、{value:^width},inwidthIt is the total width.

<: Left aligned
>: Right aligned
^: Center-aligned

name = "Alice"
 
 # Align left, total width is 10, fill with ' ' formatted_name = f"Name: {name:&lt;10}!"
 print(formatted_name)
 
 # Right-aligned, total width is 10, fill with '*' formatted_name = f"Name: {name:*&gt;10}!"
 print(formatted_name)
 
 # Align in the center, with a total width of 10, fill with '=' formatted_name = f"Name: {name:=^10}!"
 print(formatted_name)
 
 #Output Name: Alice     !
 Name: *****Alice!
 Name: ==Alice===!

2.2 Truncate string

grammar:{value:.n},innis the number of characters reserved.

long_text = "This is a very long string."
 
 # Cut to the first 10 characters formatted_text = f"Truncated: {long_text:.10}"
 print(formatted_text)
 
 #Output Truncated: This is a

3. Date and time format

3.1 Format date

usestrftimeCombination of methodsf-stringFormat date.

from datetime import datetime
 
 now = ()
 
 # Format date formatted_date = f"Today is {now:%Y-%m-%d}"
 print(formatted_date)
 
 #Output Today is 2023-10-05

3.2 Format time

from datetime import datetime
 
 now = ()
 
 # Format time formatted_time = f"The time is {now:%H:%M:%S}"
 print(formatted_time)
 
 #Output The time is 14:35:22

4. Other formatting

4.1 Scientific Counting Method

grammar:{value:.ne},innis the number of decimal places reserved.

number = 1234567890
 
 # Scientific notation method, retaining two decimal places formatted_number = f"Scientific notation: {number:.2e}"
 print(formatted_number)
 
 #Output Scientific notation: 1.23e+09

4.2 Binary, octal, hexadecimal

grammar:

Binary:{value:b}
Octal:{value:o}
hexadecimal:{value:x}(lower case) or{value:X}(capital)

number = 255
 
 # Binary binary = f"Binary: {number:b}"
 print(binary)
 
 # octal octal = f"Octal: {number:o}"
 print(octal)
 
 # hexadecimal hexadecimal = f"Hexadecimal: {number:x}"
 print(hexadecimal)
 
 #Output Binary: 11111111
 Octal: 377
 Hexadecimal: ff

4. Call functions and methods

name = "alice"
 
 # Call the title() method of the string formatted_name = f"Hello, {()}!"
 print(formatted_name)
 
 # Output Hello, Alice!

String title method:

Include the initial letters of all words like 's in it's
Difference from capitalize(): capitalize() only capitalizes the first letter of the first word of the entire string and the rest are lowercase.

5. Use dictionaries and lists

person = {"name": "Bob", "age": 30}
 
 # Access values in the dictionary info = f"{person['name']} is {person['age']} years old."
 print(info)
 
 numbers = [1, 2, 3, 4, 5]
 
 # Access elements in the list summary = f"The first number is {numbers[0]} and the last number is {numbers[-1]}."
 print(summary)
 
 #Output Bob is 30 years old.
 The first number is 1 and the last number is 5.

6. Multi-line f-string

name = "Charlie"
 age = 35
 
 # Multi-line f-string message = f"""
 Name: {name}
 Age: {age}
 """
 print(message)
 
 #Output Name: Charlie
 Age: 35

7. Nested f-string

a = 5
 b = 10
 
 #Nested f-string result = f"The sum of {a} and {b} is {f'{a + b}'}."
 print(result)
 
 # Output The sum of 5 and 10 is 15.

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