How do you declare an f-string in Python?

Question

BlackTom AI · Accepted Answer

Prefixing a string literal with f (or F) creates an f-string in Python, allowing expressions inside { } to be evaluated and interpolated into the resulting string.

1. Relevant knowledge points and concepts
- f-strings were introduced in Python 3.6.  
- An f-string is written by putting the letter f (or F) immediately before a string literal: f"..." or f'...'.  
- Any valid Python expression inside curly braces {expression} is evaluated at runtime and converted to a string representation.  
- They are more concise and readable than older formatting methods (%, str.format()).

2. Complete reasoning process step by step
- Compare the candidate forms:
  - Option b shows f"string with {expression}" — this follows the exact syntax: f prefix + string literal + braces for an expression.  
  - To confirm behaviour, take a concrete example: name = "Alice"; f"Hello {name}" evaluates the expression name and produces "Hello Alice".

3. Calculations / intermediate evaluation steps
- Example 1: name = "Alice"  
  - f"Hello {name}" -> evaluate {name} -> "Alice" -> result "Hello Alice".  
- Example 2: f"{2 + 3}" -> evaluate 2 + 3 -> 5 -> result "5".

4. Why the correct answer is correct
- Option b is the only choice that uses the required leading f before the quotes and uses { } to denote an embedded expression. That matches the formal syntax for Python f-strings.

5. Why the other options are incorrect
- Option a: "string with {expression}" — missing the f prefix; braces remain literal characters, not evaluated.  
- Option c: format("string with {expression}") — incorrect usage: format() is not called like this to interpolate; str.format() is used as "string {}".format(value) or "string {expr}".format(...).  
- Option d: "string with expression".f() — there is no .f() string method in Python; this is invalid.

6. Conclusion
- Therefore the correct choice is b: f"string with {expression}", which matches the provided answer f"string with {expression}".

How do you declare an f-string in Python?单项选择题

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