I'm a PHP Developer, i have some projects in python.
But already i done some core concepts in PHP. so is it good for reuse the those php code in python by calling via "php file.php" to return the output.
Is it's really a good practice ?
Or I should develop from scratch ?
No, it's something opposite from good practice. Typically you'll call something in the other language from Python script if that language is much quicker (usually C) or provides libraries for some complex analysis that'll be untrivial to reproduce in python (in my experience R, but that depends on the domain).
PHP doesn't give you either advantage, so it's better to redo everything in Python. Your code will be easier to maintain, requiring no PHP knowledge; it'll have better architecture; you won't have a PHP (and probably some libraries thereof) as a dependency; and, most likely, it'll be quicker.