Is there a way to determine whether a file is in YAML or JSON format?

Question

I have a Python test script that requires a configuration file. The configuration file is expected to be in JSON format.

But some of the users of my test script dislike the JSON format because it's unreadable.

So I changed my test script so that it expects the configuration file in YAML format, then converts the YAML file to a JSON file.

I would prefer that the function that loads the configuration file to handle both JSON and YAML. Is there a method in either the yaml or json module that can give me a Boolean response if the configuration file is JSON or YAML?

My workaround right now is to use two try/except clauses:

import os
import json
import yaml

# This is the configuration file - my script gets it from argparser but in
# this example, let's just say it is some file that I don't know what the format
# is
config_file = "some_config_file"

in_fh = open(config_file, "r")

config_dict = dict()
valid_json = True
valid_yaml = True

try:
    config_dict = json.load(in_fh)
except:
    print "Error trying to load the config file in JSON format"
    valid_json = False

try:
    config_dict = yaml.load(in_fh)
except:
    print "Error trying to load the config file in YAML format"
    valid_yaml = False

in_fh.close()

if not valid_yaml and not valid_json:
    print "The config file is neither JSON or YAML"
    sys.exit(1)

Now, there is a Python module I found on the Internet called isityaml that can be used to test for YAML. But I'd prefer not to install another package because I have to install this on several test hosts.

Does the json and yaml module have a method that gives me back a Boolean that tests for their respective formats?

config_file = "sample_config_file"

# I would like some method like this
if json.is_json(in_fh):
    config_dict = json.load(in_fh)

Answer 1

From your

import yaml

I conclude that you use the old PyYAML. That package only supports YAML 1.1 (from 2005) and the format specified there is not a full superset of JSON. With the YAML 1.2 (released 2009), the YAML format became a superset of JSON.

The package ruamel.yaml (disclaimer: I am the author of that package) supports YAML 1.2. You can install it in your python virtual enviroment with pip install ruamel.yaml. And by replacing PyYAML by ruamel.yaml (and not adding a package), you can just do:

import os
from ruamel.yaml import YAML

config_file = "some_config_file"

yaml = YAML()
with open(config_file, "r") as in_fh:
    config_dict = yaml.load(in_fh)

and load the file into config_dict, not caring about whether the input is YAML or JSON and no need for having a test for either format.