Python is not loading json

Question

The code runs a script using a subprocess and returns json. If I print the json, it comes back fine, but when I try to load it with json.loads, there is this error: json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

p = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
output, err = p.communicate()
outstring = str(output)
print(output) # This works
return json.loads(outstring) # This has the error

Edit: I tried outstring.json() but got this error: AttributeError: 'str' object has no attribute 'json'

What does the print(output) look like? From the error, it seems like output is the empty string. — tdelaney
– tdelaney, Commented Nov 2, 2020 at 0:27
Come to think of it, that would make the print just an empty line. What is print(repr(output))? — tdelaney
– tdelaney, Commented Nov 2, 2020 at 0:28

tdelaney · Accepted Answer · 2020-11-02 00:58:59Z

1

You print output but then try to decode outstring. In fact, you got a bytes object back from stdout. When you made it into a string, you got the string represenation of the bytes object. So, if your json is "foo", you tried to decode "b'foo'". If your command is outputing utf-8, you can just pass it to json.loads. Otherwise you need to decode it first.

p = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
output, err = p.communicate()
return json.loads(output)

or

p = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
output, err = p.communicate()
outstr = output.decode("utf-16") # or whatever encoding
return json.loads(outstr)

edited Nov 2, 2020 at 0:58

answered Nov 2, 2020 at 0:34

tdelaney

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