Can Golang multiply strings like Python can?

Yes, it can, although not with an operator but with a function in the standard library.

It would be very easy with a simple loop, but the standard library provides you a highly optimized version of it: strings.Repeat().

Your example:

x := "my new text is this long"
y := strings.Repeat("#", len(x))
fmt.Println(y)

Try it on the Go Playground.

Notes: len(x) is the "bytes" length (number of bytes) of the string (in UTF-8 encoding, this is how Go stores strings in memory). If you want the number of characters (runes), use utf8.RuneCountInString().

It has a function instead of an operator, strings.Repeat. Here's a port of your Python example, which you can run here:

package main

import (
    "fmt"
    "strings"
    "unicode/utf8"
)

func main() {
    x := "my new text is this long"
    y := strings.Repeat("#", utf8.RuneCountInString(x))
    fmt.Println(x)
    fmt.Println(y)
}

Note that I've used utf8.RuneCountInString(x) instead of len(x); the former counts "runes" (Unicode code points), while the latter counts bytes. In the case of "my new text is this long", the difference doesn't matter since all the characters are only one byte, but it's good to get into the habit of specifying what you mean:

len("ā") //=> 2
utf8.RuneCountInString("ā") //=> 1

Since this was a Python comparison question, note that in Python, the one function len counts different things depending on what you call it on. In Python 2, it counted bytes on plain strings and runes on Unicode strings (u'...'):

Python 2.7.18 (default, Aug 15 2020, 17:03:20)
>>> len('ā') #=> 2
>>> len(u'ā') #=> 1

Whereas in modern Python, plain strings are Unicode strings:

Python 3.9.6 (default, Jun 29 2021, 19:36:19) 
>>> len('ā') #=> 1

If you want to count bytes, you need to encode the string into a bytearray first:

>>> len('ā'.encode('UTF-8')) #=> 2

So Python has multiple types of string and one function to get their lengths; Go has only one kind of string, but you have to pick the length function that matches the semantics you want.

Yup. The strings package has a Repeat function.

you can use the string package. it has a repeat functionhere