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

user_1347759 0
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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)
yaml python json
4 Answers

After years I met the same trouble. I fully agree with EAFP, but still I'm trying find the best detection if the configuration file is in JSON format or YAML. In code I have methods which inform user where he did issue in json-file and where in YAML. try/except did not handle this as I really want, and my eyes are bleeding when I see those nested blocks.

This is not perfect, still has minor issues, but for me, the basic concept fits my needs. I'd say "good enough".

My solution is: find all possible standalone commas in configuration file. If config file contains standalone commas (separators in json) we have json-file, if we do not find any commas, it's yaml. In my yaml-file I use commas only in comments (between " ") and in lists (between [ ]). Maybe someone will find it usefull.

import re
from pathlib import Path

commas = re.compile(r',(?=(?![\"]*[\s\w\?\.\"\!\-\_]*,))(?=(?![^\[]*\]))')
"""
Find all commas which are standalone 
 - not between quotes - comments, answers
 - not between brackets - lists
"""
file_path = Path("example_file.cfg")
signs = commas.findall(file_path.open('r').read())

return "json" if len(signs) > 0 else "yaml"
user_118374560

I don't know if this has been answered already, but here is a way to do it

def input_parameters(file):
default_ext = '.json' #set a default extension
file_ext = pathlib.Path(file).suffix
with open(file, 'r') as f:
    if file_ext == default_ext:
        input_file = json.load(f)
    else:
        input_file = yaml.safe_load(f)
return input_file
user_129831150
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