value-based function dispatch

Question

Problem to solve

I have a method parse_doc that should dynamically determine a parsing function to parse document_id based on the value of the document_id string:

# list of files that may have different custom parser that depends arbitrarily on name:
documents = [
    "my_file.py",
    "my_file.sh",
    "another_file.txt",
    "https://some_domain.org/some_page",
]
class Parser(object):
def parse_doc(self, document_id, *args, **kwargs):

    # identify the correct parser function
    parser = return_doc_parser(document_id)
    parsed_doc = parser(document_id, *args, **kwargs)
    return parsed_doc

Proposed solution

My thought was to define a type inference function, then dispatch the appropriate function, something like the following:

import requests
import parsers
document type -> parser function handle map:
PARSER_DISPATCH = {
    "python": parsers.py_parser,
    "text": parsers.text_parser,
    "url": parsers.url_parser,
}
def return_doc_type(document_id):
    """Return custom type of document_id."""
    try:
        response = requests.get(document_id)
        if response.status_code == 200:
            url_exists = True
    except Exception:
        url_exists = False
    try:
      fp = open(document_id, "r")
      file_exists = True
    except IOError:
      file_exists = False
if file_exists and document_id.endswith(".py"):
    doc_type = "python"
elif file_exists and document_id.endswith(".txt"):
    doc_type = "text"
elif url_exists:
    doc_type = "url"
else:
    raise ValueError("no doctype identified.")
return doc_type    


class Parser(object):
def parse_doc(self, document_id, *args, **kwargs):

    doc_type = return_doc_type(document_id)
    parser = PARSER_DISPATCH[doc_type]
    parsed_doc = parser(document_id, *args, **kwargs)
    return parsed_doc

A few comments: such an informal type system seems a bit unusual, and the logic for type inference seems like it could quickly grow out of hand.

My question

Is this a reasonable approach? Are there other well-known methods to do value-based dispatch? I've googled high and low and found mostly type-based dispatch (multi-methods, multiple dispatch, method overloading) discussed.