3.2 Formatted strings
3 min read•june 24, 2024
Python's formatted strings, or , revolutionize . They allow seamless embedding of expressions and variables within , making code more readable and efficient. F-strings support various formatting options, giving developers precise control over output appearance.
Mastering f-strings opens up a world of possibilities for string formatting. From aligning text and padding output to controlling number precision and adding separators, f-strings offer powerful tools for creating polished, professional-looking output in Python programs.
Formatted Strings in Python
F-strings for embedded expressions
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- f-strings enable embedding expressions and variables inside string literals (an example of string formatting) by prefixing the string with 'f' or 'F' before the opening quotation mark
- Expressions are placed inside curly braces {} within the f-string and evaluated at runtime, with the result inserted into the string (
)f"Hello, {name}!" - f-strings support variable , allowing variables to be directly referenced inside the curly braces, with their values inserted into the resulting string (
)name = "Alice"; f"Hello, {name}!" - f-strings can contain any valid Python expression inside the curly braces, including function calls, method calls, and arithmetic operations, which are evaluated in the current context and scope (
)f"The result is: {calculate_result()}"
Format specifiers in f-strings
- Format specifiers control the display of numbers within f-strings by placing them after a colon : inside the curly braces using the syntax
[{value:format_specifier}](https://www.fiveableKeyTerm:{value:format_specifier}) - Common format specifiers for numbers include 'd' for integers (
), 'f' for floating-point numbers ([{count:d}](https://www.fiveableKeyTerm:{count:d})
), 'e' or 'E' for scientific notation ([{price:f}](https://www.fiveableKeyTerm:{price:f})
), and '%' for percentage formatting ({[value:e](https://www.fiveableKeyTerm:value:e)}
)[{percentage:%}](https://www.fiveableKeyTerm:{percentage:%}) - Precision can be specified for floating-point numbers and percentages using
after the , where n is the desired number of decimal places (.n
rounds the price to two decimal places){[price:.2f](https://www.fiveableKeyTerm:price:.2f)} - Comma separator can be added to format large numbers for better readability by using ',' after the format specifier (
formats the value with comma separators)[{value:,}](https://www.fiveableKeyTerm:{value:,})
Alignment and padding in output
- Alignment options control the positioning of the formatted value within a specified width using '<' to align left (default), '>' to align right, or '^' to center the value (
right-aligns the value with a width of 10)[{value:>10}](https://www.fiveableKeyTerm:{value:>10}) - Width is specified using a number before the alignment option to set the minimum number of characters for the formatted value (
formats the value with a minimum width of 10 characters){value:10} - Padding characters fill the empty spaces when the formatted value is shorter than the specified width, with spaces used as the default padding character
- Any character can be used as the padding character by placing it immediately after the alignment option (
right-aligns the value with a width of 10 and uses '-' as the padding character)[{value:->10}](https://www.fiveableKeyTerm:{value:->10})
- Any character can be used as the padding character by placing it immediately after the alignment option (
- Alignment, width, and padding can be combined with format specifiers (
centers the price within a width of 10 characters and rounds it to two decimal places)[{price:^10.2f}](https://www.fiveableKeyTerm:{price:^10.2f})
Additional String Operations
- allows combining multiple strings into a single string using the '+' operator or the join() method
- provide various ways to manipulate strings, such as upper(), lower(), strip(), and replace()
- String manipulation techniques include slicing, indexing, and using built-in functions like len() to work with string data
Key Terms to Review (26)
{count:d}: {count:d} is a formatting specifier used in Python's formatted strings, also known as f-strings. It allows for the insertion of a numeric value into a string, where the 'd' represents the 'decimal' format specifier. This feature provides a concise and efficient way to embed dynamic data into string literals, enhancing code readability and flexibility.
{percentage:%}: {percentage:%} is a formatting specifier used in Python's formatted strings (f-strings) to display a value as a percentage. It allows for the easy representation of numeric values as percentages, making it a useful tool for data visualization and reporting.
{price:^10.2f}: {price:^10.2f} is a format specifier used in Python's formatted strings, also known as f-strings. It is used to format a numeric value with a specific width and precision, aligning the value centrally within the specified width.
{price:f}: {price:f} is a format specifier used in Python's f-strings (formatted strings) to display a floating-point number. It allows for the precise formatting of decimal values, making it useful for displaying prices, measurements, and other numerical data with a specific number of decimal places.
{value:->10}: {value:->10} is a formatting expression used in Python's formatted strings, also known as f-strings. It allows for the insertion of a value into a string, with the value right-justified and padded with a specified character, in this case the arrow (->) symbol, to a total width of 10 characters.
{value:,}: {value:,} is a formatting technique used in Python to create formatted strings. It allows you to insert values into a string in a readable and organized way, making it easier to work with data that contains numeric values.
{value:>10}: {value:>10} is a formatting specifier used in Python's formatted strings, also known as f-strings. It is used to right-justify a value within a field of a specified width, ensuring that the value is at least 10 characters wide and aligned to the right within that field.
{value:format_specifier}: {value:format_specifier} is a syntax used in Python's formatted strings, also known as f-strings, to insert the value of a variable or expression into a string. It allows for dynamic and flexible string formatting, making it easier to create readable and informative output.
%s: %s is a placeholder used in formatted strings in Python to indicate where a string value should be inserted. This allows for dynamic string generation, making it easier to create messages or outputs that incorporate variable data. The use of %s facilitates the construction of more readable and maintainable code by separating the logic of data formatting from the actual data itself.
F-strings: F-strings, also known as formatted string literals, are a powerful feature in Python that allow for easy and efficient string formatting. They provide a concise way to embed expressions directly within string literals, making it simpler to create dynamic and customizable strings.
F'Hello, {name}!': The f-string, or formatted string literal, is a way to embed expressions inside string literals in Python. It allows you to insert variables, expressions, and other values directly into a string, making it easier to construct dynamic and readable strings.
Format specifier: A format specifier is a sequence of characters used in strings to define how values should be formatted. It allows for the integration of variables and their formatting within string literals.
Format(): The format() method in Python is a versatile tool used to format and customize the output of strings. It allows you to insert values into a string, apply various formatting options, and create dynamic and readable text output.
Formatted string literal: A formatted string literal, also known as an f-string, is a way to embed expressions inside string literals using curly braces {}. Introduced in Python 3.6, it allows for more readable and concise code.
Interpolation: Interpolation is the process of estimating or approximating a value within a range of known data points. It involves using existing information to estimate unknown values, often in the context of data analysis, numerical methods, and programming languages like Python.
New-style: New-style, in the context of Python's formatted strings, refers to a more concise and flexible way of formatting strings that was introduced in Python 3.6. This approach allows for dynamic insertion of variables and expressions directly within the string, providing a more readable and maintainable way of constructing formatted output.
Old-style: In the context of 3.2 Formatted strings, the term 'old-style' refers to a method of string formatting that was used in earlier versions of Python. This method involves using the % operator to insert values into a string, rather than the more modern and flexible f-strings or str.format() methods.
The old-style string formatting is considered less efficient and more cumbersome compared to the newer techniques, but it is still supported in Python for backward compatibility.
Placeholder: A placeholder is a temporary or substitute value that is used in a string or other data structure to represent a value that will be determined or inserted later. It serves as a placeholder for information that is not yet available or known at the time of writing the code.
Price:.2f: The term `price:.2f` is a format specifier used in formatted strings in Python to control the presentation of floating-point numbers. Specifically, it ensures that a floating-point number is represented as a string with exactly two decimal places, making it ideal for displaying prices or monetary values. This formatting is crucial in providing clear and professional outputs, especially in applications involving financial data.
Replacement field: A replacement field is a placeholder within a formatted string that gets replaced by specific values during string formatting. It is denoted by curly braces {} and can include optional format specifications.
Str.format(): The str.format() method is a powerful tool in Python that allows you to insert values into a string in a more flexible and readable way than traditional string concatenation. It provides a way to format strings by replacing placeholders with specified values, making it a versatile and efficient approach for creating dynamic and customized output.
String concatenation: String concatenation is the process of combining two or more strings into a single string. This fundamental operation allows developers to create dynamic strings by merging fixed text with variable content, enhancing how information is presented and formatted. It's particularly useful when constructing messages, formatting output, or preparing data for further processing.
String Literals: String literals are a way to represent text data in programming languages like Python. They are a fundamental data type used to store and manipulate textual information within a program.
String Manipulation: String manipulation refers to the process of modifying, manipulating, or transforming the contents of a string in a programming language like Python. It involves techniques and operations that allow developers to extract, modify, or analyze the data within a string.
String Methods: String methods are built-in functions in Python that allow you to perform various operations and manipulations on string data types. These methods provide a wide range of functionalities, from modifying the case of characters to searching, splitting, and joining strings, making it easier to work with and process textual information.
Value:e: 'value:e' is a formatting specification in Python that is used within formatted strings to represent floating-point numbers in exponential notation. This syntax allows developers to easily control the presentation of numerical values, making it particularly useful when dealing with very large or very small numbers that require a concise format for better readability. Understanding this notation is important as it enhances the ability to format output precisely, which can be crucial in data analysis and reporting.