Go and namespaces: is it possible to achieve something similar to Python?

Question

I wonder if there is a way to use namespaces in the Go language in a similar way as Python does.

In Python if I have the following files containing functions:

/a.py
    def foo():
/b.py
    def bar():

I can access foo and bar in a third Python file as following:

import a
a1 = a.foo()
import b
b1 = b.bar()

I had some difficulties finding some documentation on namespaces with the Go language. How are namespaces implemented in go? With package and import? Or is import dedicated to external libraries?

I think I understood that for each package there should be a dedicated directory. I wonder if this is absolutely mandatory, because it can become impractical whenever a high granularity of modules is the best way to engineer a certain idea. In other words, I would like to avoid using one directory per package (for internal use).

Answer 1

Go's equivalent to Python modules are packages. Unlike Python modules that exist as a single file, a Go package is represented by a directory. While a simple package might only include a single source file in the directory, larger packages can be split over multiple files.

So to take your Python example, you could create a file $GOPATH/src/a/a.go with the following contents:

package a

import "fmt"

func Foo() {
    fmt.Println("a.Foo")
}

In your main program, you can call the function like so:

package main

import "a"

func main() {
    a.Foo()
}

One thing to note is that only exported types and functions in a will be available externally. That is, types and functions whose names begin with a capital letter (which is why I renamed foo to Foo).

If you don't want to set up a Go workspace, you can also use relative paths for your imports. For instance, if you change the import in the main program to import "./a", then the source code for the a package can be located at a/a.go relative to the main program.