It was accepted in no time. thank you!! But i also needed do a slight modification. ~~~~~

def dfs(node,m):
    visited[node]=1
    if a[node-1]==1:
        m=m+1
    else:
        m=0
    if m>k:
        yield 0
    for v in g[node]:
        if visited[v]!=1:
            yield dfs(v,m) #it was just dfs(v,m) before
    if node in leaf:
        leaf[node]=1
    yield 1

~~~~~ without the modification yield was stopping the complete process if it was hitting the leaf node. So now it works. But the same modification if i do on a normal recursion the program is giving WA even for smaller values. I think it has to do something with being stackless. I am keeping this here just so that everyone keeps in mind some slight changes may be needed to be done if you use this version. Thanks again though. :) i am gonna use this code from now on.

I'm trying to get this to work but can't seem to, trying to make it work with some very simple recursive functions and I just get errors. The following code gives me TypeError: unsupported operand type(s) for +: 'generator' and 'generator' on both python 2 and 3:

@bootstrap
def recurse(n):
  if (n < 2):
    yield n
  yield recurse(n-1) + recurse(n-2)

print(recurse(20))

An even more trivial function that dodges the above error will still error out with File "main.py", line 18, in wrappedfunc to = stack[-1].send(to):

@bootstrap
def recurse(n):
  if (n == 0):
    yield 1
  yield recurse(n-1)

Is there something obvious I'm missing?

Wow that's really simple and clever!!

I am so glad I asked this question here. somehow when I searched it on google all answers were like switch to c++ or set recursion limit. But now when I dig deeper specially in codeforces blogs I found the topic of threading mentioned but very vague. All this blogs were about getting stuck on a specific problem statement. So I did not click on it before.

its sad that even it is an old trick its not very well known as no blog/resource actually exists dedicated to this topic. Thank you so much for answering :)

This code gives Memory limit exceeded in pypy3. You have any trick for pypy3?