PyPy Compressed Sparse Row

csr.py

from array import array

class Graph:
    def __init__(self, N):
        self.h = array('I', [1 << 30]) * N
        self.l = array('I')
        self.e = array('I')
    def connect(self, u, v):
        p = self.h[u]
        self.h[u] = len(self.l)
        self.l.append(p)
        self.e.append(v)
    def iter(self, u):
        it = GraphIter()
        it.l = self.l
        it.e = self.e
        it.i = self.h[u]
        return it

class GraphIter:
    __slots__ = ('l', 'e', 'i')
    def __iter__(self):
        return self
    def __next__(self):
        if self.i == 1 << 30:
            raise StopIteration
        v = self.e[self.i]
        self.i = self.l[self.i]
        return v