Package

The code described in the following section have now been made available in a separate package. Please see this repository for details: https://github.com/Xaldew/yasnippet-radical-snippets.

Old Answer

(defun python-args-to-google-docstring (text &optional make-fields)
  "Return a reST docstring format for the python arguments in yas-text."
  (let* ((indent (concat "\n" (make-string (current-column) 32)))
         (args (python-split-args text))
     (nr 0)
         (formatted-args
      (mapconcat
       (lambda (x)
         (concat "   " (nth 0 x)
             (if make-fields (format " ${%d:arg%d}" (incf nr) nr))
             (if (nth 1 x) (concat " \(default " (nth 1 x) "\)"))))
       args
       indent)))
    (unless (string= formatted-args "")
      (concat
       (mapconcat 'identity
          (list "" "Args:" formatted-args)
          indent)
       "\n"))))

(defun python-args-to-google-docstring (text &optional make-fields)
  "Return a reST docstring format for the python arguments in yas-text."
  (let* ((indent (concat "\n" (make-string (current-column) 32)))
         (args (python-split-args text))
     (nr 0)
         (formatted-args
      (mapconcat
       (lambda (x)
         (concat "   " (nth 0 x)
             (if make-fields (format " ${%d:arg%d}" (cl-incf nr) nr))
             (if (nth 1 x) (concat " \(default " (nth 1 x) "\)"))))
       args
       indent)))
    (unless (string= formatted-args "")
      (concat
       (mapconcat 'identity
          (list "" "Args:" formatted-args)
          indent)
       "\n"))))

# -*- mode: snippet -*-
# Insert Google style docstring and function definition.
# name: Python Google style Docstring
# key: defg
# type: snippet
# contributor: Xaldew
# --
def ${1:name}($2):
    \"\"\"$3
    ${2:$(python-args-to-google-docstring yas-text t)}
    ${5:Returns:
        $6
}
    \"\"\"
    ${0:$$(let ((beg yas-snippet-beg)
            (end yas-snippet-end))
    (yas-expand-snippet
      (buffer-substring-no-properties beg end) beg end)
        (delete-trailing-whitespace beg (- end 1)))}

There is still an issue with using this inside nested indentation, e.g., within classes or as nested functions. In those cases the docstring is erroneously indented an extra time for some reason. I'll update this post if I manage to fix that.

# -*- mode: snippet -*-
# Insert Google style docstring and function definition.
# name: Python Google style Docstring
# key: defg
# type: snippet
# contributor: Xaldew
# --
def ${1:name}($2):
    \"\"\"$3
    ${2:$(python-args-to-google-docstring yas-text t)}
    ${5:Returns:
        $6
}
    \"\"\"
    ${0:$$(let ((beg yas-snippet-beg)
                (end yas-snippet-end))
        (yas-expand-snippet
          (buffer-substring-no-properties beg end) beg end
              (quote ((yas-indent-line nil) (yas-wrap-around-region nil))))
            (delete-trailing-whitespace beg (- end 1)))}

There is still an issue with using this inside nested indentation, e.g., within classes or as nested functions. In those cases the docstring is erroneously indented an extra time for some reason. I'll update this post if I manage to fix that.

The snippet should now work inside other scopes by forbidding yasnippet from auto-indenting the second expansion.