MonotonicExpandingSequence

MonotonicExpandingSequence.py

# A bit of cleverness to create a new sequence for infinite iterators
from collections.abc import Sequence

class MonotonicExpandingSequence(Sequence):
    def __init__(self, iterator):
        self.iterator = iterator
        self._cache = []
        
    def __getitem__(self, index):
        while len(self._cache) <= index:
            self._cache.append(next(self.iterator))
        return self._cache[index]
    
    def __len__(self):
        return len(self._cache)
      
    def __contains__(self, num):
        i = 0
        while True:
            if self[i] == num:
                return True
            elif self[i] > num:
                return False
            else:
                i += 1
                
# Usage, e.g.: 
# primes = MonotonicExpandingSequence(get_all_primes())
# if 257 in primes: ...
# if 258 in primes: ...
# n = primes[100]