an extensible multi-markup reader in less than 100 lines of python code

markup.py

# (c) miraculixx, licensed as by the terms of WTFPL, http://www.wtfpl.net/txt/copying/
# License: DO WHATEVER YOU WANT TO with this code. 
#
# THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
#
from io import StringIO

from contextlib import contextmanager
import re

def markup(file_or_str, parsers=None, direct=True, on_error='warn', default=None, msg='could not read {}',
           **kwargs):
    """
    a safe markup file reader, accepts json and yaml, returns a dict or a default
    Usage:
        file_or_str = filename|file-like|markup-str
        # try, return None if not readable, will issue a warning in the log
        data = markup(file_or_str)
        # try, return some other default, will issue a warning in the log
        data = markup(file_or_str, default={})
        # try and fail
        data = markup(file_or_str, on_error='fail')
    Args:
        file_or_str (None, str, file-like): any file-like, can be
           any object that the parsers accept
        parsers (list): the list of parsers, defaults to json.load, yaml.safe_load,
           json.loads
        direct (bool): if True returns the result, else returns markup (self). then use
           .read() to actually read the contents
        on_error (str): 'fail' raises a ValueError in case of error, 'warn' outputs a warning to the log, 
           and returns the default, 'silent' returns the default. Defaults to warn
        default (obj): return the obj if the input is None or in case of on_error=warn or silent
        **kwargs (dict): any kwargs passed on to read(), any entry that matches a parser
            function's module name will be passed on to the parser
    Returns:
        data parsed or default
        markups.exceptions contains list of exceptions raised, if any
    """
    import json
    import yaml
    import logging

    parsers = parsers or (json.load, yaml.safe_load, json.loads)
    # path-like regex
    # - \/?                  leading /, optional
    # - (?P<path>\w+/?)*     any path-part followed by /, repeated 0 - n times
    # - (?P<ext>(\w*\.?\w*)+ any file.ext, at least once
    pathlike = lambda s: re.match(r"^\/?(?P<path>\w+/?)*(?P<ext>(\w*\.?\w*))$", s)

    @contextmanager
    def fopen(filein, *args, **kwargs):
        # https://stackoverflow.com/a/55032634/890242
        if isinstance(filein, str) and pathlike(filein):  # filename
            with open(filein, *args, **kwargs) as f:
                yield f
        elif isinstance(filein, str):  # some other string, make a file-like
            yield StringIO(filein)
        else:
            # file-like object
            yield filein

    throw = lambda ex: (_ for _ in ()).throw(ex)
    exceptions = []

    def read(**kwargs):
        if file_or_str is None:
            return default
        for fn in parsers:
            try:
                with fopen(file_or_str) as fin:
                    if hasattr(fin, 'seek'):
                        fin.seek(0)
                    data = fn(fin, **kwargs.get(fn.__module__, {}))
            except Exception as e:
                exceptions.append(e)
            else:
                return data
        # nothing worked so far
        actions = {
            'fail': lambda: throw(ValueError("Reading {} caused exceptions {}".format(file_or_str, exceptions))),
            'warn': lambda: logging.warning(msg.format(file_or_str)) or default,
            'silent': lambda: default,
        }
        return actions[on_error]()

    markup.read = read
    markup.exceptions = exceptions
    return markup.read(**kwargs) if direct else markup

def raises(fn, wanted_ex):
    try:
        fn()
    except Exception as e:
        assert isinstance(e, wanted_ex), "expected {}, raised {} instead".format(wanted_ex, e)
    else:
        raise ValueError("did not raise {}".format(wanted_ex))
    return True

if __name__ == '__main__':
    import sys
    from pprint import pprint

    if len(sys.argv) > 1:
       pprint(markup(sys.argv[1], on_error='fail'))
    else:
       print("testing...")
       assert markup('foo: bar') == {'foo': 'bar'}
       assert markup('{"foo": "bar"}') == {'foo': 'bar'}
       assert markup(StringIO("foo: bar")) == {'foo': 'bar'}
       #assert markup('test.txt') == {'foo': 'bar'}
       assert raises(lambda : markup('xtest.txt', on_error='fail') == {'foo': 'bar'}, ValueError)
       assert isinstance(markup('xtest.txt', on_error='silent', default=markup).exceptions[0], FileNotFoundError)
       assert markup('failed: - bar') is None
       assert markup('failed: - bar', default={}) == {}
       assert raises(lambda : markup('failed: - bar', on_error='fail'), ValueError)
       assert markup('failed: - bar', on_error='silent') is None
       assert markup('failed: - bar', on_error='silent', default="nothing") == 'nothing'
       assert markup('', default="nothing") == 'nothing'
       assert lambda : markup('.', on_error='silent', default="nothing") == 'nothing'
       assert lambda : markup('.', on_error='fail')
       assert markup('foo: bar', direct=False) == markup and markup.read() == {'foo': 'bar'} 
       print("ok. use as python markup.py '<file or markup>'")