Python – Inserts a docstring attribute into a python file

Inserts a docstring attribute into a python file… here is a solution to the problem.

Inserts a docstring attribute into a python file

We are using Napoleonic style docstrings for python modules. However, additional properties need to be automatically populated in the document strings named Data Owner and DAL Owner so that the given function looks like this

def func(self, arg1=None, arg2=None):
Returns the timeseries for the specified arg1 and arg2.
    arg1: argument 1
    arg2: argument 2
    DataFrame containing timeseries of arg1 for arg2.

DAL Owner: Team IT
Data Owner: Team A

These additional properties and their values for a given function are provided in a separate CSV file. My idea was to have a script (awk, sed?). ) will

  • Extracts all function names in a given Python file. It can be easily done in Python
  • For those function names, check that the owner exists in the CSV file, and if so, create a mapping of the function name and owner. Doable

Now, here’s the part where I haven’t figured it out and don’t know the best way forward. For a given function name and owner, I need to go back to the python file and add the owner to the docstring if it exists. I’m thinking about some kind of awk script, but I’m not quite sure

  • Find the function that matches the pattern
  • For that mode, see if doctsring exists with triple quotes after the closing parenthesis
  • If docstring is present, add two extra lines for the owner before the closing triple quotes
  • If docstring does not exist, insert two lines for owners between tripe quotations in the line after the function declaration.

I know it’s a lot of steps, but anyone can provide insight into the previous 4 bullet points to insert additional properties into docstrings given functions, properties, and python files. Linux utilities like sed, awk would be more useful, or should I go the Python route. Are there other options that are easier to implement.


The process for assigning a new docstring in AST is:

  1. Use >ast.get_docstring to get an existing doc string
  2. Create a new AST node with the modified content
  3. If the existing dostring is None, a new node is inserted at the beginning of the parent node body
  4. If there is an existing docstring, replace its node with a new one
  5. 使用unparse * Tools from Cpython Tools to generate new source code (you may need to download this from GitHub – make sure you get a version that matches your python version).

Here is some sample code:

$  cat                            
import ast                                                                               
import io
from unparse import Unparser

class DocstringWriter(ast. NodeTransformer):
    def visit_FunctionDef(self, node):
        docstring = ast.get_docstring(node)
        new_docstring_node = make_docstring_node(docstring)
        if docstring:
            # Assumes the existing docstring is the first node 
            # in the function body.
            node.body[0] = new_docstring_node
            node.body.insert(0, new_docstring_node)
        return node

def make_docstring_node(docstring):
    if docstring is None:
        content = "A new docstring"
        content = docstring + " -- amended"
    s = ast. Str(content)
    return ast. Expr(value=s)

if __name__ == "__main__":
    tree = ast.parse(open("").read())
    transformer = DocstringWriter()
    new_tree = transformer.visit(tree)
    buf = io. StringIO()
    Unparser(new_tree, buf)

$  cat 
def foo():

def bar():
    """A docstring."""

$  python 

def foo():
    'A new docstring'

def bar():
    'A docstring. -- amended'

(I answered a similar question myself for python 2.7, here)


* Starting with Python 3.9, the ast module provides a unparse instead The function used by the unparse tool: src = ast.unparse(new_tree).

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