String Formatting in Go

Go follows the printf tradition from the C language. In my opinion, string formatting/interpolation in Go is less elegant than Python's f-strings, unfortunately.

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fmt.Printf and fmt.Sprintf

• fmt.Printf() - Prints a formatted string to standard out.
• fmt.Sprintf() - Returns the formatted string

Both follow the printf tradition: "formatting verbs" like %v and %d control how each value is rendered.

Default Representation

The %v variant prints any value in a default format. It can be used as a catchall.

s := fmt.Sprintf("I am %v years old", 10)
// I am 10 years old

s := fmt.Sprintf("I am %v years old", "way too many")
// I am way too many years old

fmt.Sprintf is a string interpolation function, similar to Python's f-strings. The %v substring uses the type's default formatting, which is often what you want.

const name = "Kim"
const age = 22
s := fmt.Sprintf("%v is %v years old.", name, age)
// s = "Kim is 22 years old."

The equivalent Python code:

name = "Kim"
age = 22
s = f"{name} is {age} years old."
# s = "Kim is 22 years old."

If you want to print in a more specific way, you can use the following formatting verbs:

String

s := fmt.Sprintf("I am %s years old", "way too many")
// I am way too many years old

Integer

s := fmt.Sprintf("I am %d years old", 10)
// I am 10 years old

Float

s := fmt.Sprintf("I am %f years old", 10.523)
// I am 10.523000 years old

// The ".2" rounds the number to 2 decimal places
s := fmt.Sprintf("I am %.2f years old", 10.523)
// I am 10.52 years old

Boolean

The %t verb formats a boolean value.

s := fmt.Sprintf("Is Go fun? %t", true)
// Is Go fun? true

If you're interested in all the formatting options, you can look at the fmt package's docs.