Replace range with itertools & remove future dep

Author: karlfloersch

ethereum/chain.py

@@ -1,5 +1,5 @@
 import time
-from builtins import range
+from itertools import count, islice
 from ethereum import utils
 from ethereum.utils import parse_as_bin, big_endian_to_int
 from ethereum import parse_genesis_declaration
@@ -264,7 +264,7 @@ def add_block(self, block):
                         break
                     b = self.get_parent(b)
                 replace_from = b.header.number
-                for i in range(replace_from, 2**63 - 1):
+                for i in islice(count(), replace_from, 2**63 - 1):
                     log.info('Rewriting height %d' % i)
                     key = 'block:' + str(i)
                     orig_at_height = self.db.get(key) if key in self.db else None
@@ -325,7 +325,7 @@ def get_chain(self, frm=None, to=2**63 - 1):
         if frm is None:
             frm = int(self.db.get('GENESIS_NUMBER')) + 1
         chain = []
-        for i in range(frm, to):
+        for i in islice(count(), frm, to):
             h = self.get_blockhash_by_number(i)
             if not h:
                 return chain

requirements.txt

@@ -4,7 +4,6 @@ PyYAML
 repoze.lru
 pbkdf2
 pycryptodome>=3.3.1
-future==0.16.0
 scrypt
 rlp>=0.4.7
 https://github.com/ethereum/ethash/tarball/master