? Python String Formatting

? Quick Overview

String formatting lets you insert variables and expressions into a string in a clean, readable way. Python supports several approaches, including modern f-strings and the older str.format() method, which help you control text, numbers, alignment and overall layout.

? Key Concepts

Use f-strings (f"...{expression}...") in Python 3.6+ for concise formatting.
Use the format() method for older Python versions or when f-strings are not available.
Apply positional and keyword placeholders for better control in templates.
Format numbers with a fixed number of decimal places (e.g., {pi:.2f}).
Control padding and alignment (left, right, center) to build neat tables and reports.

? Syntax and Theory

An f-string is written by prefixing a string with f, for example: f"My name is {name}". Any valid Python expression inside {...} will be evaluated and converted to a string.

The format() method works by using placeholders inside a string: "My name is {}".format(name). You can also use numbered placeholders ({0}, {1}) or named placeholders ({n}, {a}).

For numbers, you can add a format specifier after a colon, such as {pi:.2f} (2 decimal places) or {pi:10.3f} (width 10, 3 decimal places). Alignment uses < (left), > (right) and ^ (center) along with a width, for example {text:<10}.

? Code Examples

? Basic f-string example

name = "Alice"
age = 25
message = f"My name is {name} and I am {age} years old."
print(message)

? Using the format() method

name = "Alice"
age = 25
message = "My name is {} and I am {} years old.".format(name, age)
print(message)

? Positional and keyword arguments

name = "Alice"
age = 25

message1 = "Name: {0}, Age: {1}".format(name, age)
message2 = "Name: {n}, Age: {a}".format(n=name, a=age)

print(message1)
print(message2)

? Formatting numbers

pi = 3.14159

print(f"Pi rounded: {pi:.2f}")          # 3.14
print("Pi rounded: {:.3f}".format(pi))  # 3.142

? Padding and alignment with f-strings

text = "Python"

print(f"{text:<10}X")   # Left align
print(f"{text:>10}X")   # Right align
print(f"{text:^10}X")   # Center align

? Live Output and Explanation

? What these examples do

The basic f-string and format() examples both print: My name is Alice and I am 25 years old.
The positional/keyword example prints: Name: Alice, Age: 25 twice, once using positions and once using named placeholders.
The number formatting example rounds 3.14159 to: 3.14 (2 decimal places) and 3.142 (3 decimal places).
The alignment example prints the word Python inside a field of width 10, with an extra X character showing where the padding ends: left-aligned, right-aligned, and centered.

Together, these examples show how formatting helps you build clean, readable console output and properly aligned text for tables, logs, and reports.

✅ Tips

Prefer f-strings for readability and efficiency in Python 3.6+.
Use .format() when you must support Python versions earlier than 3.6.
Control decimals and alignment for clean output in reports, tables, and logs.
Always validate variable types before formatting to avoid errors.
Do not forget the f prefix when using f-strings, otherwise {...} will not be evaluated.
When using format(), make sure placeholders and arguments match to avoid IndexError or KeyError.

? Practice Tasks

Create a greeting message using an f-string with your name and favorite programming language.
Format a floating-point number to 2 decimal places using both an f-string and the format() method.
Align three different words in a table-like layout using f-string alignment (<, >, ^).
Use keyword arguments in format() to neatly display your name, age, and city.