The iter data unpack function.

    Example 1:
        In[1]: source = 'abc'
        In[2]: a, b = safe_unpack(source, 2)
        In[3]: print(a, b)
        a b

    Example 2:
        In[1]: source = 'abc'
        In[2]: a, b, c, d = safe_unpack(source, 4)
        In[3]: print(a, b, c, d)
        a b None None

def unpack(iterable, count, fill=None):
    """
    The iter data unpack function.

    Example 1:
        In[1]: source = 'abc'
        In[2]: a, b = safe_unpack(source, 2)
        In[3]: print(a, b)
        a b

    Example 2:
        In[1]: source = 'abc'
        In[2]: a, b, c, d = safe_unpack(source, 4)
        In[3]: print(a, b, c, d)
        a b None None
    """
    iterable = list(enumerate(iterable))
    cnt = count if count <= len(iterable) else len(iterable)
    results = [iterable[i][1] for i in range(cnt)]

    # results[len(results):len(results)] = [fill for i in range(count-cnt)]
    results = merge(results, [fill for i in range(count-cnt)])
    return tuple(results)