Converting Markov Chain Python Script to PHP. Not sure of what some of the equivalent functions are in PHP

Question

I've seen this Markov Chain gibberish detector written in response to another question on Stackoverflow and I would like to convert it to PHP, I'm not looking for someone to do this for me, but I am confused over portions of the Python code that I have no knowledge of. I've looked at the python docs but it confuses me even further.

1. What is the PHP equivalent of yield?

   def ngram(n, l):
   """ Return all n grams from l after normalizing """
   filtered = normalize(l)
   for start in range(0, len(filtered) - n + 1):
       yield ''.join(filtered[start:start + n])
   

2. What exactly is xrange? There is a PECL extension, however I would prefer a pure PHP implementation? Would this be possible?

   counts = [[10 for i in xrange(k)] for i in xrange(k)]
   
   for i, row in enumerate(counts):
   s = float(sum(row))
   for j in xrange(len(row)):
       row[j] = math.log(row[j] / s)
   

3. What does assert do? Is it the equivalent of throwing an Exception?

   assert min(good_probs) > max(bad_probs)
   

4. Python Pickle, is that essentially serialize?

   pickle.dump({'mat': counts, 'thresh': thresh}, open('gib_model.pki', 'wb'))
   

Thanks for any help.

---

Edit: typos.

Answer 1

1. What is the PHP equivalent of yield?

There is no equivalent to yield in PHP. yield is used in generator functions - a special class of function that returns a result but retains its state.

For example:

def simple_generator(start=0, end=100):
    while start < end:
        start += 1
        yield start
gen = simple_generator()
gen() # 1
gen() # 2
gen() # 3

You can do something similar in PHP like so:

class simple_generator {
    private $start;
    private $end;
    function __construct($start=0, $end=100) {
        $this->start = $start;
        $this->end = $end;
    }
    function __call() {
        if($this->start < $this->end) {
            $this->start++;
            return $start;
        }
    }
}
gen = simple_generator();
gen(); // 1
gen(); // 2

2. What exactly is xrange?

xrange behaves just like range, but uses a generator function. This is a performance tweak for working with very large lists or when memory is tight.

3. What does assert do? Is it the equivalent of throwing and Exception?

Yes. Beware - it is not the same as PHP's assert - which is a really fun vector for attacks on your software.

4. Python Pickle, is that essentially serialize?

Yes.

Answer 2

1. xrange returns an iterator. This is different from range which returns a list. Both behave mostly in the same fashion so just use it like you use range.

2. Yes

3. Yes