PHP writting 'null' for JSON file written by Python

Question

I am trying to send JSON information from Python to PHP through a JSON file data.json, based on the content of the Stack Overflow question/answer here. I am running this code all on an Apache web server on Raspberry Pi 3.

Here is my code:

Python

import sys, json, random # I know I don't need sys and random to run this, but I was using these in my previous code.
data = {'fruit':['oranges', 'apples', 'peaches'], 'age':12}
with open('data.json', 'w') as outfile:
    json.dump(data, outfile)

When run, this program worked fine and exited with code 0.

JSON file

{"age": 12, "fruit": ["oranges", "apples", "peaches"]}

As you can see, my Python worked perfectly and the output is identical to the data variable in my python code. On second thought, the order is backward, although I don't think this matters.

PHP

Now, this is where the problem is:

<?php
$string = file_get_contents("data.json");
$json_a = json_decode($string, true);
$arr = array();
foreach ($json_a as $key) {
    array_push($arr,json_decode($key[0],true));
}
echo json_encode($arr);
?>

When run, the program exited with code 0 but outputed:

[null,null]

Does anyone have an idea why this is, or is this just the way JSON works?

json_decode is only valid on JSON strings and the json_decode's in the loop are not given JSON strings: the outer usage of json_decode has already turned all the JSON text into a PHP object graph (of arrays and arrays in arrays and values within those arrays). — user2864740
– user2864740, Commented Nov 22, 2017 at 22:06
How should I approach the problem if I am using lists, or is this not possible? data['age'] is not a string. — Tiskolin
– Tiskolin, Commented Nov 22, 2017 at 22:07
What's your actual desired output here? I can't really tell what it is you're trying to achieve in the PHP step. — iainn
– iainn, Commented Nov 22, 2017 at 22:09
That gives me oranges[null,null]. Thanks, but is there some way to make the entire loop compatible with lists? — Tiskolin
– Tiskolin, Commented Nov 22, 2017 at 22:10

RamC · Accepted Answer · 2017-11-23 06:40:51Z

The original code with issues:

<?php
$string = file_get_contents("data.json");
$json_a = json_decode($string, true);
$arr = array();
foreach ($json_a as $key) {
    // No need to use json_decode again
    // as it is already converted to an array
    // by the inital json decode statement
    array_push($arr,json_decode($key[0],true));
}
echo json_encode($arr);
?>

Pretty printed PHP Array which is stored inside $json_a:

Array
(
    [age] => 12
    [fruit] => Array
        (
            [0] => oranges
            [1] => apples
            [2] => peaches
        )

)

The problem:

In the original script, json_decode was used on an already decoded variable/array which returned nothing and hence null was appended to your list.

Code walkthrough: During the first iteration of the foreach loop,

$key will have the value 12 - which is a string

During the second iteration of the foreach loop,

$key will have the value - which is an Array

Array
(
    [0] => oranges
    [1] => apples
    [2] => peaches
)

The corrected code for printing all the fruits:

<?php
$string = file_get_contents("data.json");
$json_a = json_decode($string, true);
$arr = array();
foreach ($json_a['fruit'] as $key) {
    array_push($arr,$key);
}
echo json_encode($arr);
?>

The above snippet returns ["oranges","apples","peaches"]

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