How Can I Achieve Python's `string.format()` Functionality in Go?

Equivalent of Python string.format in Go?

In Python, string interpolation is often done using the format() function, which allows for the insertion of values into a string template. In Go, there are several ways to achieve similar functionality.

fmt.Sprintf

The most straightforward option is to use the fmt.Sprintf function, which takes a format string and a variable number of arguments. The arguments are inserted into the format string in the order they appear. For example:

fmt.Sprintf("File %s had error %s", myfile, err)

However, this method does not allow for the swapping of argument order in the format string, which is sometimes necessary for internationalization (I18N) purposes.

text/template

Go also provides the text/template package, which allows for more complex string interpolation. However, it requires the use of a template, which can be more verbose than simply using fmt.Sprintf.

tmpl, _ := template.New("errmsg").Parse("File {{.File}} has error {{.Error}}")
tmpl.Execute(&msg, params)

strings.Replacer

For a more compact and flexible solution, consider using the strings.Replacer type. It allows you to define a mapping from keys to replacement strings. The keys can be included in the format string using curly braces, and the Replacer will replace them with the corresponding replacement strings.

r := strings.NewReplacer("{file}", file, "{error}", err)
fmt.Println(r.Replace("File {file} had error {error}"))

This method allows for the swapping of argument order in the format string and can be easily extended to handle different types of values.

Explicit Argument Indices

Finally, Go's fmt package also supports explicit argument indices, which can be used multiple times to reference the same argument. This allows for a more concise way of inserting the same value into a format string multiple times.

fmt.Printf("File %d has error %d\n", 1, 1)

This approach provides the most flexibility in terms of ordering and inserting the same value multiple times.

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