Use an f-string when output must combine text with values such as numbers or variables. Prefix the string with f and place expressions inside curly braces: f'Hello, {name}'. Python evaluates each embedded expression and inserts its value. section 2.5 section 2.3
Choose f-strings over older formatting approaches when you need readable, expression-driven output:
- Avoid concatenating strings and integers with +; place the number directly inside the expression braces. section 2.5
- Evaluate expressions inside braces, including arithmetic and method calls, such as {x*2} or {y.capitalize()}. section 2.5
- Use formatting specifications after a colon inside braces when values need alignment, as in {first:#<10}. section 2.5
name = 'world'
x = 100
y = 'abcd'
f'x * 2 = {x*2}, and y.capitalize() is {y.capitalize()}'
Compare direct variable interpolation with arithmetic and method evaluation in one executable example. section 2.5
name = 'world'
first = 'Reuven'
last = 'Lerner'
f'Hello, {first:#<10} {last:#>10}' #1
Inspect alignment formatting by applying fill characters and width specifications to two values. section 2.5
