A faster method to generate a nested list from a template?

[DJTB]

Hi all,

I'm new to Python. I'm trying to create a fast function to do the following:

t = [['a1','a2'],['b1'],['c1'],['d1']]
l = [1,2,3,4,5]
>>> create_nested_list(t,l)
[[1, 2], [3], [4], [5]]

t is some sort of template. This is what I have now:

def create_nested_list(template,l_orig):
    '''Uses a template to create a new list
    
    t = [['a1','a2'],['b1'],['c1'],['d1']]
    l = [1,2,3,4,5]
    >>> create_nested_list(t,l)
    [[1, 2], [3], [4], [5]]
    '''
    
    tl = map(len, template)
    # Input size check
    if reduce(lambda x,y: x+y, tl) != len(l_orig):
        raise "Wrong input size"
    
    l = l_orig
    new_nested_list = []
    for x in tl:
        q = []
        i = 0
        while i < x:
            q.append(l.pop(0))
            i += 1
        new_nested_list.append(q)
    return new_nested_list 

I'd like to know if it is possible to make this faster (using Python magic I
don't know of yet), because this function will be called a lot
('constantly').

Thanks in advance,
Stan.