trickle.py

istr = """for i in some_array:"""

ostr = """\
{0}for(0 => int {1}; {1}<{2}.cap(); {1}++){{
{0}    {2}[{1}];\n{0}}}"""


def check_is_loopform(istr):
    # returns non None only if everything seems ok.

    # does not support tabs, but could. I don't use tabs so meh.
    # some preprocessing, count spaces to the left, store this
    restr = istr.lstrip()
    spaces = len(istr) - len(restr)
    restr = restr.strip()

    if (not restr.startswith("for ")):
        print("must start with keyword for")
        return

    elements = restr.split()
    if (not len(elements) == 4):
        print("must take form:  for i in some_array:")
        print("got: {}  instead".format(restr))
        return
    
    if (not elements[2] == "in"):
        print("missing the  in   keyword")
        return

    if (not restr.endswith(":")):
        print("must end with colon")
        return

    return [spaces, elements]

def perform_replacement(istr):
    content = check_is_loopform(istr)
    if not content:
        return 

    amount_space = " "*content[0]
    print('{} spaces,  do: {}'.format(*content))
    print(ostr.format(amount_space, content[1][1], content[1][3][:-1]))


perform_replacement(istr)

"""outputs

for(0 => int i; i<some_array.cap(); i++){
    some_array[i];
}

"""