--- title: "4.18 f-Strings – Part 2" description: "In addition to inserting variables and expressions, **f-strings** support **format specifications** that control how values are displayed. Using format specifiers, you can control the number of decimal places, alignment, field width, padding, percentages, and much more. Format specifiers are written…" url: "https://edcret.in/docs/python-programming/strings-python/4-18-f-strings-part-2/" updated: "2026-07-29" category: Python Programming / Strings --- # 4.18 f-Strings – Part 2 In addition to inserting variables and expressions, **f-strings** support **format specifications** that control how values are displayed. Using format specifiers, you can control the number of decimal places, alignment, field width, padding, percentages, and much more. Format specifiers are written after a colon (`:`) inside the curly braces. F-strings combine the simplicity of variable substitution with powerful formatting capabilities, making them the preferred choice for producing professional and readable output. --- ## Syntax ``` f"{expression:format_specifier}" ``` ### Components | Component | Description | | --- | --- | | `f` | Indicates a formatted string literal. | | `{}` | Placeholder containing the value or expression. | | `:` | Separates the expression from the format specification. | | `format_specifier` | Controls how the value is displayed. | --- ## Example 1: Formatting Decimal Places **main.py** ``` price = 49.9876 print(f"Price: ${price:.2f}") ``` ### Output ``` Price: $49.99 ``` ### Explanation - `{price:.2f}` formats the floating-point number. - `.2f` displays exactly two digits after the decimal point. - Python rounds the value automatically. --- ## Example 2: Displaying a Percentage **main.py** ``` marks = 0.92 print(f"Percentage: {marks:.0%}") ``` ### Output ``` Percentage: 92% ``` ### Explanation - `%` converts the decimal value into a percentage. - `.0%` displays no digits after the decimal point. - `0.92` becomes `92%`. --- ## Example 3: Right Alignment **main.py** ``` word = "Python" print(f"|{word:>15}|") ``` ### Output ``` | Python| ``` ### Explanation - `>` aligns the text to the right. - `15` specifies the total field width. - Extra spaces are added before the text. --- ## Example 4: Left Alignment **main.py** ``` word = "Python" print(f"|{word:<15}|") ``` ### Output ``` |Python | ``` ### Explanation - `<` aligns the text to the left. - Spaces are added after the text. - The total width is 15 characters. --- ## Example 5: Center Alignment **main.py** ``` title = "Menu" print(f"|{title:^20}|") ``` ### Output ``` | Menu | ``` ### Explanation - `^` centers the text. - Spaces are added equally on both sides whenever possible. - The field width is 20 characters. --- ## Example 6: Padding with Zeros **main.py** ``` number = 42 print(f"{number:05}") ``` ### Output ``` 00042 ``` ### Explanation - `5` specifies the total width. - Missing positions are filled with zeros. - The final output contains five characters. --- ## Example 7: Thousands Separator **main.py** ``` population = 12345678 print(f"{population:,}") ``` ### Output ``` 12,345,678 ``` ### Explanation - `,` inserts commas as thousands separators. - Large numbers become easier to read. - The numeric value remains unchanged. --- ## Example 8: Formatting Multiple Values **main.py** ``` name = "Alice" score = 96.75 print(f"Student: {name}, Score: {score:.1f}") ``` ### Output ``` Student: Alice, Score: 96.8 ``` ### Explanation - Multiple placeholders can appear in the same f-string. - The name is inserted directly. - The score is rounded to one decimal place. --- ## Example 9: Evaluating Complex Expressions **main.py** ``` a = 8 b = 3 print(f"Average = {(a + b) / 2:.2f}") ``` ### Output ``` Average = 5.50 ``` ### Explanation - The expression is evaluated first. - The result is then formatted using `.2f`. - Both calculation and formatting happen inside the f-string. --- ## Example 10: Combining Alignment and Formatting **main.py** ``` item = "Book" price = 15.5 print(f"|{item:<12}| ${price:>7.2f}") ``` ### Output ``` |Book | $ 15.50 ``` ### Explanation - `{item:<12}` left-aligns the item name. - `{price:>7.2f}` right-aligns the price. - This style is commonly used when displaying tables and invoices. --- # Common Mistakes ### 1. Forgetting the Colon Before the Format Specifier **Incorrect** ``` price = 49.95 print(f"{price.2f}") ``` ### Output ``` SyntaxError: invalid decimal literal ``` **Reason** The colon (`:`) separates the expression from the format specification. **Correct** ``` print(f"{price:.2f}") ``` --- ### 2. Using a Format Specifier on an Incompatible Type **Incorrect** ``` name = "Alice" print(f"{name:.2f}") ``` ### Output ``` ValueError: Unknown format code 'f' for object of type 'str' ``` **Reason** `.2f` can only be used with numeric values. **Correct** ``` print(f"{name}") ``` --- ### 3. Forgetting the Field Width **Incorrect** ``` word = "Python" print(f"|{word:>}|") ``` ### Output ``` ValueError: Format specifier missing precision ``` **Reason** Alignment symbols should normally be followed by a field width. **Correct** ``` print(f"|{word:>10}|") ``` --- ### 4. Expecting Formatting to Change the Original Variable **Incorrect** ``` price = 49.9876 print(f"{price:.2f}") print(price) ``` ### Incorrect Expectation ``` 49.99 49.99 ``` ### Actual Output ``` 49.99 49.9876 ``` **Reason** Formatting only changes how the value is displayed. The original variable remains unchanged. --- # Best Practices - Use f-strings for all new Python programs. - Apply format specifiers to improve readability. - Use `.2f` for displaying floating-point values such as prices or measurements. - Use alignment specifiers when printing tables or reports. - Keep expressions inside f-strings simple and readable. --- # Key Points to Remember - Format specifiers are written after a colon (`:`) inside `{}`. - `.2f` displays two decimal places. - `%` converts a decimal value to a percentage. - `<`, `>`, and `^` control left, right, and center alignment. - Commas (`,`) add thousands separators. - Formatting changes only the displayed output, not the original variable. - F-strings are the recommended formatting method in modern Python.