How to pretty print variables

Question

Is there something like Ruby's awesome_print in Go?

For example in Ruby you could write:

require 'ap'
x = {a:1,b:2} // also works for class
ap x

the output would be:

{ 
  "a" => 1,
  "b" => 2
}

closest thing that I could found is Printf("%#v", x)

If an external package is acceptable, consider [pretty](http://godoc.org/github.com/kr/pretty#example-package). — Mark, Nov 25 '14 at 03:06
I tried both go-spew and pretty and found that pretty loses prettiness after some depth of nested structs while go-spew keeps it. — ufukty, Apr 04 '23 at 12:37

Simon Whitehead · Accepted Answer · 2014-11-25T03:03:20.253

123

If your goal is to avoid importing a third-party package, your other option is to use json.MarshalIndent:

x := map[string]interface{}{"a": 1, "b": 2}
b, err := json.MarshalIndent(x, "", "  ")
if err != nil {
    fmt.Println("error:", err)
}
fmt.Print(string(b))

Output:

{
    "a": 1,
    "b": 2
}

Working sample: http://play.golang.org/p/SNdn7DsBjy

edited Nov 25 '14 at 03:03

answered Nov 25 '14 at 02:47

Simon Whitehead

63,300
9
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1

Testing multiple levels of indention. https://play.golang.org/p/d3nO4Rht90 – Xeoncross Dec 19 '16 at 15:23
1

Marshal gets intro trouble when there is a custom struct (unsupported type error). Any easy way to fix that? – etang Aug 09 '17 at 00:18
@etang You would have to show a simple example for me to give you a better answer (perhaps in the Playground?). I imagine you'll have to implement one of the JSON package interfaces for unmarshalling your type if it becomes complex. – Simon Whitehead Aug 09 '17 at 00:40

score 27 · Answer 2 · answered Nov 25 '14 at 02:44

Nevermind, I found one: https://github.com/davecgh/go-spew

// import "github.com/davecgh/go-spew/spew"
x := map[string]interface{}{"a":1,"b":2}
spew.Dump(x)

Would give an output:

(map[string]interface {}) (len=2) {
 (string) (len=1) "a": (int) 1,
 (string) (len=1) "b": (int) 2
}

score 14 · Answer 3 · answered May 13 '21 at 11:00

14

If you want pretty coloured output, you can use pp.

https://github.com/k0kubun/pp

import "github.com/k0kubun/pp"
...
pp.Print(m)

answered May 13 '21 at 11:00

Ruben S

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1

good one for pretty print – Krishna ps Dec 12 '21 at 09:40

score 4 · Answer 4 · answered May 04 '21 at 11:37

4

I just wrote a simple function based on Simons answer:

func dump(data interface{}){
    b,_:=json.MarshalIndent(data, "", "  ")
    fmt.Print(string(b))
}

answered May 04 '21 at 11:37

MSS

3,520
24
29

I do this all the time, +1. though I usually panic on the error – erik258 Feb 24 '22 at 03:53

score 3 · Answer 5 · answered Aug 13 '18 at 11:00

3

I came up to use snippet like this:

func printMap(m map[string]string) {
    var maxLenKey int
    for k, _ := range m {
        if len(k) > maxLenKey {
            maxLenKey = len(k)
        }
    }

    for k, v := range m {
        fmt.Println(k + ": " + strings.Repeat(" ", maxLenKey - len(k)) + v)
    }
}

The output will be like this:

short_key:       value1
really_long_key: value2

Tell me, if there's some simpler way to do the same alignment.

answered Aug 13 '18 at 11:00

andstepko

111
1
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5

You can use `fmt.Printf("%*s: %s", maxLenKey, k, v)` to avoid the `strings.Repeat` call and all that concatenation. – Eric Lindsey Nov 11 '18 at 08:24

How to pretty print variables

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