How can the built-in range function take a single argument or three?

Question

I would like to know, if anyone can tell me, how the range function can take either: a single argument, range(stop), or range(start, stop), or

Answer 1

class xrangeIterator:

def __init__(self,xrange_obj):

    self._xrange_obj=xrange_obj


def __next__(self):

    self.copy_gen=self._xrange_obj._result

    for i in self.copy_gen:

        return i

    raise StopIteration

class xrange:

def __init__(self,*args):

    self._args=args

    self.start,self.step=0,1

    self._repr_string=None

    for i in self._args:

        if type(i) is not int:

            raise TypeError("Cannot interprate '{}' as integer!".format(type(i).__name__))


    if self._length(self._args)<1:

        raise TypeError( "xrange Must have at least one argument")


    elif self._length(self._args)==1:

        self.stop=self._args[0]

        self._repr_string="xrange(0,{})".format(self.stop)

        self._result=self._xrange(self.start-self.step,self.stop-self.step,self.step)

    elif self._length(self._args)==2:

        self.start=self._args[0]

        self.stop=self._args[1]

        self._result=self._xrange(self.start-self.step,self.stop-self.step,self.step)

    elif self._length(self._args)==3:

        self.step=self._args[2]

        self.start=self._args[0]

        self.stop=self._args[1]

        self._result=self._xrange(self.start-self.step,self.stop-self.step,self.step)


    else:

        raise TypeError("xrange expected at most three arguments,got {}".format(self._length(self._args)))


def __repr__(self):

    if self._length(self._args)==1:

        return self._repr_string

    return "xrange{}".format(self._args)

def __iter__(self):

    return xrangeIterator(self)


def _length(self,n):

    counter=0

    for i in n:

        counter+=1

    return counter


def _xrange(self,start,stop,step):

    if step==0:

            raise ValueError("Argument 3 should not be zero!")

    if startstop and step<0:

            start+=step

            yield start