How to turn recursion into a loop to avoid maximum recursion error

Question

The following is a snippet of code from my program:

def get_data(self):
    self.position = self.hfile.tell()/self.sizeof_data


    try:
        self.iq = scipy.fromfile(self.hfile, dtype=self.datatype, count=self.block_length)


    except MemoryError:
        print "End of File"
    else:
        self.iq_fft = self.dofft(self.iq)
    x = self.iq_fft

        maximum = np.argmax(x)
        average = np.mean(x)

    print "\nAvage Value: ", average 

        #set up Get Data loop
        loops = self.files/self.block_length
        self.counter += 1
        count = self.counter
        count += 1
        print "\nCOUNT: ", count
        #print "\nloop: ", loops

    if count == loop:
        raise SystemExit #Exits program gracefully
    else:   
        self.get_data()



def dofft(self, iq):
    N = len(iq)

    iq_fft = scipy.fftpack.fftshift(scipy.fft(iq))       # fft and shift axis


    iq_fft = scipy.log10(abs((iq_fft))) # convert to decibels, adjust power
    # adding 1e-15 (-300 dB) to protect against value errors if an item in iq_fft is 0

    return iq_fft

It works great unless loop is greater than 989, then the whole thing blows up. I have seen some talk about how in Python recursion is limited to 999, so I know that's the problem, but how can I rewrite the loop to avoid the error? The loop has potential to get pretty large so I don't think using the setrecursionlimit() function is a good idea.

It's pretty difficult to answer this without seeing the recursive version! What would you be iterating over, what do you do on each iteration, and how do you decide you've finished? — jonrsharpe
– jonrsharpe, Commented Mar 24, 2014 at 23:22
" I have seen some talk about how in Python recursion is limited to 999, so I know that's the problem" - that is called assuming, and it's one of the top reasons myself and most engineers I've met have written bugs. In the future, even if something is very likely, make sure it's the reason. — Vinay
– Vinay, Commented Mar 24, 2014 at 23:27
I don't understand why you would call it iteratively anyway; every time you call it, it stomps on self.position, self.iq, self.iq_fft, self.counter... I think you need to make a self.next() method which returns these values for each block, and raises StopIteration when it reaches end of file, then you can iterate through blocks on your class. — Hugh Bothwell
– Hugh Bothwell, Commented Mar 25, 2014 at 0:20

justhalf · Accepted Answer · 2014-03-25 02:22:19Z

1

I don't understand why you wrote this as recursion when it's clearly an iterative process (reading a file block by block, as I understand it).

def get_data(self):
    for count in range(self.files/self.block_length):
        self.position = self.hfile.tell()/self.sizeof_data

        try:
            self.iq = scipy.fromfile(self.hfile, dtype=self.datatype, count=self.block_length)
        except MemoryError:
            print "End of File"

        self.iq_fft = self.dofft(self.iq)
        x = self.iq_fft

        maximum = np.argmax(x)
        average = np.mean(x)

        print "\nAverage Value: ", average 

        self.counter += 1
        print "\nCOUNT: ", count
    raise SystemExit

answered Mar 25, 2014 at 2:22

justhalf

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Hugh Bothwell · Accepted Answer · 2014-03-25 00:50:55Z

It's a bit hard to tell exactly what you are trying to accomplish, but it looks like you need something like

import scipy as sp
import scipy.fftpack as sf

def db_fft(block):
    res = sp.fft(block)         # compute FFT
    res = sf.fftshift(res)      # shift axis
    res = sp.log10(abs((res)))  # convert to db, adjust power
    return res

class BlockFFT:
    def __init__(self, fname, dtype=sp.float64, blocksize=256*256):
        self.hfile     = open(fname, "rb")
        self.dtype     = dtype      # data type
        self.blocksize = blocksize  # number of items per step

    def next(self):
        try:
            block = scipy.fromfile(self.hfile, dtype=self.dtype, count=self.blocksize)
            fft   = db_fft(block)
            return fft, sp.argmax(fft), sp.mean(fft)
        except MemoryError:
            self.hfile.close()
            raise StopIteration()

def main():
    for fft, max_, avg_ in BlockFFT("myfile.dat"):
        # now do something with it
        pass

if __name__=="__main__":
    main()

Blue Ice · Accepted Answer · 2014-03-24 23:25:34Z

0

Maybe this:

while count != loop
    #run whatever is in get data
else
    raise SystemExit

If you provided more information, though, I might go for a for loop instead.

answered Mar 24, 2014 at 23:25

Blue Ice

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Jack burridge · Accepted Answer · 2014-03-24 23:28:57Z

-1

Get your function to return a bound function then run it until no function is returned. You can bind a function using partial in functools.

from functools import partial
def yourfunc(test):
    # code
    if answer:
        return answer
    return partial(yourfunc,boundvariable)

answered Mar 24, 2014 at 23:28

Jack burridge

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