fästrings

F-strings, short for formatted string literals, are a feature of the Python programming language that enable inline expression evaluation within string literals. Introduced in Python 3.6 as part of PEP 498, they provide a concise and readable syntax for combining text with values.

Syntax and conversion: An f-string is created by prefixing a string literal with the letter f or F. Expressions can appear inside braces, for example f"Hello, {name}". To include a literal brace, double it: {{ or }}. A conversion specifier can follow a colon to apply a conversion, e.g., !r for repr, !s for str, !a for ascii. A format spec following a colon applies to the value, as in f"{value:.2f}".

Expressions inside braces are evaluated at runtime using the current local and global scope. They can access variables, attributes, indices, and even call functions, e.g., f"Sum: {values[0] + values[1]}". Complex expressions are allowed but statements are not; you cannot put multi-statement code inside braces. Since Python 3.8, the walrus operator can appear inside an expression.

Limitations and notes: f-strings must be valid Python expressions; to include braces literally you must escape. They are evaluated when the string is created, so care is needed when including user-supplied input, as arbitrary code could be run through expressions. Performance is generally good, often faster than concatenation or older formatting methods.

Comparison and usage: F-strings are preferred in modern Python for readability and performance. They can replace the format method and percent formatting in many cases, while maintaining a concise syntax.