Golang equivalent to Python Formatted String using F-strings

Question

In python one can use f-string to format strings like this

name1 = 'Ele'
name2 = 'Ben'
name3 = 'Frank'
age = 45

print(f"My name is {name1} but I also get called {name2} and at times {name3}. Generally I prefer {name1} and my age is {age}")

what is golang's equivalent to this? where I can specify exactly which variable at what spot

currently this is all I see with golang, but it creates repeating variables unnecessarily like below

name1 := "Ele"
name2 := "Ben"
name3 := "Frank"
age := 45

message := fmt.Sprintf("My name is %s but I also get called %s and at times %s. Generally I prefer %s and my age is %d", name1, name2, name3, name1, age)

fmt.Println(message)

Imagine if I need to repeat a variable multiple times in the same string, I will have to keep repeating it and then need to monitor the position of the variable always to make sure they align correctly

Is there a way similar to f-string in python for golang?

so no way to specify exactly the variable? only way is to use %s and %d all over? — uberrebu
– uberrebu, Commented Jan 16, 2022 at 5:38
Before Python 3.6, that's (mainly) how it was done in Python, too. Also C and many other languages. — MattDMo
– MattDMo, Commented Jan 16, 2022 at 5:40

chuckx · Accepted Answer · 2022-01-16 09:45:52Z

1

You can use text/template.

It's a bit overkill for this simple example, but it can be worth the overhead when dealing with complex templates, lots of output, etc.

package main

import (
    "bytes"
    "fmt"
    "log"
    "text/template"
)

func main() {
    data := fdata{
        "Name1": "Ele",
        "Name2": "Ben",
        "Name3": "Frank",
        "Age":   45,
    }
    format := "My name is {{.Name1}} but I also get called {{.Name2}} and at times {{.Name3}}. Generally I prefer {{.Name1}} and my age is {{.Age}}."

    result, err := fstring(format, data)
    if err != nil {
        log.Fatalf("fstring() failed: %v", err)
    }

    fmt.Println(result)
}

type fdata map[string]interface{}

func fstring(format string, data fdata) (string, error) {
    t, err := template.New("fstring").Parse(format)
    if err != nil {
        return "", fmt.Errorf("error creating template: %v", err)
    }
    output := new(bytes.Buffer)
    if err := t.Execute(output, data); err != nil {
        return "", fmt.Errorf("error executing template: %v", err)
    }
    return output.String(), nil
}

Output:

My name is Ele but I also get called Ben and at times Frank. Generally I prefer Ele and my age is 45.

Go Playground

edited Jan 16, 2022 at 9:45

answered Jan 16, 2022 at 7:29

chuckx

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2 Comments

uberrebu Over a year ago

pretty good!..in the situation where i just need the string with the formatted variable values, how can i get the final string generated the fastest/simplest way? seems i have to go through multiple lines of code for your answer

chuckx Over a year ago

You can compartmentalize the interaction with text/template by implementing a helper function. And you can use a map instead of struct. (I've updated the answer to demonstrate these). But at the end of the day, Go isn't Python, so feature parity isn't a given and the code to accomplish a given task will be different.

General Grievance · Accepted Answer · 2023-11-06 14:30:36Z

0

I have used fmt.Println("My name is " + name), I have declared var name prior as my name and it worked. But I tried doing fmt.Print("My name is " + name "and my age is" + age) which is creating an error

Edit: I got this as in go lang you cannot use string with an int, so you have to write as:

package main

import "fmt"

func main() {
    //var name string = "Srijit"
    var name string = "Srijit"
    fmt.Println("My name is " + name)
    name = "Sam"
    fmt.Println("My name is " + name)

    num := 23

    fmt.Println("My name is "+name, "and my age is", num)
}

See I have changed +num to ,num (it does not allow string to num)

edited Nov 6, 2023 at 14:30

General Grievance

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answered Nov 5, 2023 at 12:26

Srijit Bhattacharya

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1 Comment

carbocation Over a year ago

fmt.Print("My name is " + name "and my age is" + age) creates an error because it is invalid syntax. You correctly place a + in front of name, but you failed to place a + after name. In contrast, this works: fmt.Println("My name is "+name+" and my age is", num)

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