Load data from php file into python

Question

I have a huge php file that contains a number of arrays

<?php
$quadrature_weights = array();
$quadrature_weights[2] = array(
 1.0000000000000000,
 1.0000000000000000);
$quadrature_weights[3] = array(
 0.8888888888888888,
 0.5555555555555555,
 0.5555555555555555);
$quadrature_weights[4] = array(
 0.6521451548625461,
 0.6521451548625461,
 0.3478548451374538,
 0.3478548451374538);
?>

The real file contains 64 quadrature_weights and the actual number of decimals of the numbers inside the arrays is in the order of 200 (I have reduced the number here for readability).

I would like to load this file into python and determine how many decimals to keep. Lets say i decide to keep 4 decimals the output should be a dictionary (or some other container) like this

quadrature_weights = {
 2: [1.0000, 
 1.0000],
 3: [0.8888,
 0.5555,
 0.5555],
 4: [0.6521,
 0.6521,
 0.3478,
 0.3478]
 }

I am not familiar with php and quite frankly I have no idea how to do this. I suppose it would be possible read every single line and then do some sort of "decoding" manually but I was really hoping to avoid that.

• deceze: Option #1: somehow parse PHP code in Python to extract the data. ☹️ Option #2: modify that PHP code and let it output the data in some easy format like JSON (echo json_encode($quadrature_weights);), then read that into Python. ☺️
• user5479362: Does this answer your question? Read a plain text file with php
• mortysporty: @9ilsdx 9rvj 0lo it seems I need to know how to use php for that to work... so no. But thank you for the suggestion.
• deceze: Note though that "deciding how many decimals to keep" isn't a thing with floats. You can type "1.0000" all you want, the machine is going to forget about those zeros immediately, because they're irrelevant to the value of the number. 1.0 is exactly the same as 1.000000000, and floats don't store the useless information of how many zeros you typed.
• mortysporty: @deceze ♦ Option #2 seems like the most viable route given what I know, Regarding the number of decimals, your point is valid for 1.00000 but not for the other numbers.

Answer 1

If the number of decimals is in the 200s in the PHP file, then PHP will truncate that and there is a 100% guarantee you will not get the same numbers out if you let PHP parse those arrays and output JSON to then use in Python.

Personally, I'd read the file line-by-line and parse it in Python using regular expressions. Something along the lines of:

import re
quadrature_weights = {}
max_decimals = 6
with open("/path/to/file.php") as phpfile:
 key = None
 
 for line in phpfile:
 match_key = re.search("\[(\d+)\]", line)
 if match_key:
 key = match_key.group(1)
 quadrature_weights[key] = []
 continue
 match_value = re.search("([\d.]+)", line)
 if match_value:
 quadrature_weights[key].append(
 round(float(match_value.group(1)), max_decimals)
 )
print(quadrature_weights)

With an input file like yours, the output of this will be (indented for readability):

{
 '2': [1.0, 1.0],
 '3': [0.888889, 0.555556, 0.555556],
 '4': [0.652145, 0.652145, 0.347855, 0.347855]
}

If you want to always keep the correct number of decimals, even if the number is "1.0000000000000", then you should treat the numbers as strings:

match_value = re.search("([\d.]+)", line)
if match_value:
 value = match_value.group(1)
 period = value.index('.')
 max_length = period + 1 + max_decimals
 quadrature_weights[key].append(value[0:max_length])

With this change, the dict will look like (indented for readability):

{
 '2': ['1.000000', '1.000000'],
 '3': ['0.888888', '0.555555', '0.555555'],
 '4': ['0.652145', '0.652145', '0.347854', '0.347854']
}

Then you can convert the values to float when you actually need to use the numerical values for calculations.

• mortysporty: It didnt work straight away but I will tinker a bit with it and see if I can get it to work. Thank you.
• rickdenhaan: @mortysporty I updated my answer so that it now contains working code. Specifically, re.match() should have been re.search() and I've added the float conversion and rounding to a specific number of decimals (as specified in max_decimals))