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For a project I am working on, I need to use a lot of primes, frequently. To do this, I added a cache to Will Ness's prime sieve, that stores already generated primes so getting them is quick. How can I improve this code?

def prime_sieve(): # postponed sieve, by Will Ness
 for c in (2,3,5,7): # original code David Eppstein,
 yield c
 sieve = # Alex Martelli, ActiveState Recipe 2002
 ps = prime_sieve() # a separate base Primes Supply:
 p = next(ps) and next(ps) # (3) a Prime to add to dict
 q = p*p # (9) its sQuare
 for c in count(9,2): # the Candidate
 if c in sieve: # c’s a multiple of some base prime
 s = sieve.pop(c) # i.e. a composite ; or
 elif c < q:
 yield c # a prime
 continue
 else: # (c==q): # or the next base prime’s square:
 s=count(q+2*p,2*p) # (9+6, by 6 : 15,21,27,33,...)
 p=next(ps) # (5)
 q=p*p # (25)
 for m in s: # the next multiple
 if m not in sieve: # no duplicates
 break
 sieve[m] = s # original test entry: ideone.com/WFv4f

class cached_primes:
 def __init__(self):
 self.prime_gen = prime_sieve()
 self.vals = [2]
 next(self.prime_gen)

 def get(self, start=2, end=float('inf')):
 vals = self.vals

 lo = self.get_ind(start)
 if vals[-1] >= end:
 hi = self.get_ind(end)
 yield from islice(vals, lo, hi)
 return
 else:
 while vals[-1] < end:
 if len(vals) > lo:
 bound = len(vals)
 yield from takewhile(lambda p: p <=end, islice(vals, lo, bound))
 lo = bound
 vals.append(next(self.prime_gen))
 hi = self.get_ind(end)
 yield from islice(vals, lo, hi)

 def get_ind(self, x):
 if x <= 2:
 return 0
 vals = self.vals
 B = x/log(x)
 if x < 17:
 return bisect(vals, x, 0, min(len(vals), int(B)))
 return bisect(vals, x, int(B), min(len(vals), int(1.25506*B)))