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```def isOdd(integer):
#assert isinstance(integer, int)
return integer % 2 == 1

def isEven(integer):
#assert isinstance(integer, int)
return integer % 2 == 0

def _list_to_string(li):
return ''.join(map(str, li))

class GrayCode(object):
def __init__(self, nbits):
self._nbits = nbits
self._grayCode = []
self.__generate()

def __getitem__(self, i):
return self._grayCode[i]

def __str__(self):
return str(self._grayCode)

__repr__ = __str__

def __iter__(self):
return self._grayCode.__iter__()

def __generate(self):
li = [0 for i in xrange(self._nbits)]
self._grayCode.append(_list_to_string(li))

for term in xrange(2, (1<<self._nbits)+1):
if isOdd(term):
for i in xrange(-1,-(self._nbits),-1):
if li[i]==1:
li[i-1]=li[i-1]^1
break

if isEven(term):
li[-1]=li[-1]^1

self._grayCode.append(_list_to_string(li))

class GrayCodeIterator(object):
def __init__(self, nbits):
self._nbits = nbits

def __iter__(self):
li = [0 for i in xrange(self._nbits)]
yield _list_to_string(li)

for term in xrange(2, (1<<self._nbits)+1):
if isOdd(term):
for i in xrange(-1,-(self._nbits),-1):
if li[i]==1:
li[i-1]=li[i-1]^1
break

if isEven(term):
li[-1]=li[-1]^1

yield _list_to_string(li)

if __name__=='__main__':
d = 4
codes=GrayCode(d)
print '%d digits gray codes:' % d
print codes
print 'Using Iterator:'
#for c in GrayCode(20):
#    print c
for c in GrayCodeIterator(20):
print c
```

### History

• revision 3 (15 years ago)
• previous revisions are not available