+++ slug = "string-formatting" title = "String Formatting" section = "Text" summary = "f-strings turn values into readable text at the point of use." doc_path = "/tutorial/inputoutput.html#formatted-string-literals" see_also = [ "strings", "logging", "csv-data", "values", ] +++

Formatted string literals, or f-strings, exist because programs constantly need to turn values into human-readable text. They keep the expression next to the words it explains.

Format specifications after : control presentation details such as width, alignment, padding, and precision. This separates the value being computed from the way it should be displayed.

Use f-strings for most new formatting code. They relate directly to expressions: anything inside braces is evaluated, then formatted into the surrounding string.

:::program

name = "Ada"
score = 9.5
rank = 1

message = f"{name} scored {score}"
print(message)

row = f"{rank:>2} | {name:<8} | {score:05.1f}"
print(row)

print(f"{score = }")

:::

:::cell An f-string evaluates expressions inside braces and inserts their string form into the surrounding text. This is clearer than joining several converted values by hand.

name = "Ada"
score = 9.5
rank = 1

message = f"{name} scored {score}"
print(message)

Ada scored 9.5

:::

:::cell Format specifications after : control display without changing the underlying values. Here the rank is right-aligned, the name is left-aligned, and 05.1f zero-pads the score to a width of five characters with one decimal place.

row = f"{rank:>2} | {name:<8} | {score:05.1f}"
print(row)

 1 | Ada      | 009.5

:::

:::cell The debug form with = is useful while learning or logging because it prints both the expression and the value.

print(f"{score = }")

score = 9.5

:::

:::note

• Use f"..." strings for most new formatting code.
• Expressions inside braces are evaluated before formatting.
• Format specifications after : control alignment, width, padding, and precision. :::