--- title: "4.17 f-Strings – Part 1" description: "An **f-string** (formatted string literal) is the modern and recommended way to format strings in Python. An f-string is created by placing the letter **`f`** or **`F`** immediately before the opening quotation mark. Expressions enclosed within curly braces (`{}`) are…" url: "https://edcret.in/docs/python-programming/strings-python/4-17-f-strings-part-1/" updated: "2026-07-29" category: Python Programming / Strings --- # 4.17 f-Strings – Part 1 An **f-string** (formatted string literal) is the modern and recommended way to format strings in Python. An f-string is created by placing the letter **`f`** or **`F`** immediately before the opening quotation mark. Expressions enclosed within curly braces (`{}`) are evaluated and their values are inserted directly into the string. Compared to `%` formatting and the `format()` method, f-strings are easier to read, require less code, and generally execute faster. F-strings are widely used in modern Python programs for displaying variables, calculations, and expressions. --- ## Syntax ``` f"Text {expression}" ``` or ``` F"Text {expression}" ``` ### Components | Component | Description | | --- | --- | | `f` or `F` | Prefix indicating a formatted string literal. | | `{}` | Placeholder containing a variable or expression. | | `expression` | Variable, value, or expression evaluated by Python. | --- ## Example 1: Formatting a Variable **main.py** ``` name = "Alice" print(f"Hello, {name}!") ``` ### Output ``` Hello, Alice! ``` ### Explanation - The `f` prefix creates an f-string. - `{name}` is replaced by the value of the variable `name`. - The formatted string is printed. --- ## Example 2: Formatting Multiple Variables **main.py** ``` name = "John" age = 25 print(f"Name: {name}, Age: {age}") ``` ### Output ``` Name: John, Age: 25 ``` ### Explanation - Both variables are placed inside curly braces. - Python replaces each placeholder with its corresponding value. - The resulting string is displayed. --- ## Example 3: Using Expressions **main.py** ``` a = 10 b = 20 print(f"Sum = {a + b}") ``` ### Output ``` Sum = 30 ``` ### Explanation - The expression `a + b` is evaluated. - Python inserts the result into the string. - Expressions can be written directly inside `{}`. --- ## Example 4: Performing Calculations **main.py** ``` length = 5 width = 8 print(f"Area = {length * width}") ``` ### Output ``` Area = 40 ``` ### Explanation - The multiplication expression is evaluated. - The computed result replaces the placeholder. - No separate variable is required. --- ## Example 5: User Input **main.py** ``` name = input("Enter your name: ") print(f"Welcome, {name}!") ``` ### Sample Input ``` Alice ``` ### Output ``` Welcome, Alice! ``` ### Explanation - The user enters a name. - The value stored in `name` is inserted into the f-string. - The greeting is displayed. --- ## Example 6: Mixing Different Data Types **main.py** ``` product = "Laptop" quantity = 3 price = 599.99 print(f"Product: {product}, Quantity: {quantity}, Price: ${price}") ``` ### Output ``` Product: Laptop, Quantity: 3, Price: $599.99 ``` ### Explanation - Strings, integers, and floating-point numbers can all be inserted. - Python automatically converts values to string form when necessary. - The output is easy to read. --- ## Example 7: Calling Functions Inside an f-String **main.py** ``` word = "python" print(f"{word.upper()}") ``` ### Output ``` PYTHON ``` ### Explanation - Function calls can be placed inside `{}`. - `upper()` converts the string to uppercase. - The returned value is inserted into the string. --- ## Example 8: Using an Uppercase Prefix **main.py** ``` language = "Python" print(F"Learning {language}") ``` ### Output ``` Learning Python ``` ### Explanation - Both `f` and `F` create formatted string literals. - They behave exactly the same. - The choice is based on coding style. --- ## Example 9: Formatting a Boolean Expression **main.py** ``` age = 18 print(f"Eligible: {age >= 18}") ``` ### Output ``` Eligible: True ``` ### Explanation - The comparison `age >= 18` is evaluated. - The Boolean result is inserted into the string. - Expressions inside `{}` can return any data type. --- ## Example 10: Checking the Result Type **main.py** ``` name = "Python" result = f"Welcome {name}" print(result) print(type(result)) ``` ### Output ``` Welcome Python ``` ### Explanation - An f-string creates a new string. - The formatted result is stored in `result`. - Its data type is `str`. --- # Common Mistakes ### 1. Forgetting the `f` Prefix **Incorrect** ``` name = "Alice" print("Hello, {name}") ``` ### Output ``` Hello, {name} ``` **Reason** Without the `f` prefix, Python treats `{name}` as ordinary text. **Correct** ``` print(f"Hello, {name}") ``` --- ### 2. Using Undefined Variables **Incorrect** ``` print(f"Hello, {username}") ``` ### Output ``` NameError: name 'username' is not defined ``` **Reason** The variable inside `{}` must already exist. **Correct** ``` username = "Alice" print(f"Hello, {username}") ``` --- ### 3. Forgetting the Curly Braces **Incorrect** ``` name = "Alice" print(f"Hello, name") ``` ### Output ``` Hello, name ``` **Reason** Variables must be enclosed within `{}`. **Correct** ``` print(f"Hello, {name}") ``` --- ### 4. Assuming an f-String Changes the Variable **Incorrect** ``` name = "Alice" f"Hello, {name}" print(name) ``` ### Output ``` Alice ``` **Reason** An f-string creates a new string. It does not modify the original variable. --- # Best Practices - Prefer f-strings over `%` formatting and `format()` in modern Python programs. - Use meaningful variable names inside f-strings. - Keep expressions simple for better readability. - Use f-strings for messages, reports, and user-friendly output. - Remember to include the `f` prefix before the opening quotation mark. --- # Key Points to Remember - An f-string is created using the `f` or `F` prefix. - Values inside `{}` are evaluated automatically. - Variables, expressions, and function calls can be placed inside `{}`. - F-strings produce a new string of type `str`. - F-strings are more readable than `%` formatting and `format()`. - The `f` prefix is mandatory. - F-strings are the recommended formatting method in modern Python.