def test_read(self):
max_items = 10
item = [1] * 10
class ImageReadIterator(six.Iterator):
def __init__(self):
self.num_items = 0
def __iter__(self):
return self
def __next__(self):
if (self.num_items < max_items):
self.num_items += 1
return item
raise StopIteration
next = __next__
handle = rw_handles.ImageReadHandle(ImageReadIterator())
for _ in range(0, max_items):
self.assertEqual(item, handle.read(10))
self.assertFalse(handle.read(10))
python类Iterator()的实例源码
def chunked(iterable, n):
"""
Split iterable in chunks of size n, where each chunk is also an iterator.
for chunk in chunked(range(10), 3):
for element in chunk:
print element
>>> it = chunked(range(7), 2)
>>> list(map(tuple, it))
[(0, 1), (2, 3), (4, 5), (6,)]
:param iterable iterable: Any iterable, e.g. list, range, ...
:param n: Chunk size
:return: Chunked iterable
:rtype: Iterator over iterators
"""
it = iter(iterable)
while True:
chunk_it = itt.islice(it, n)
try:
first_el = next(chunk_it)
except StopIteration:
return
yield itt.chain((first_el,), chunk_it)
def flatmap(func, iterable):
"""
Map function to iterable and flatten.
>>> f = lambda n: str(n) * n
>>> list( flatmap(f, [1, 2, 3]) )
['1', '2', '2', '3', '3', '3']
>>> list( map(f, [1, 2, 3]) ) # map instead of flatmap
['1', '22', '333']
:param function func: Function to map on iterable.
:param iterable iterable: Any iterable, e.g. list, range, ...
:return: Iterator of iterable elements transformed via func and flattened.
:rtype: Iterator
"""
return itt.chain.from_iterable(map(func, iterable))
def test_iterator():
class myiter(six.Iterator):
def __next__(self):
return 13
assert six.advance_iterator(myiter()) == 13
class myitersub(myiter):
def __next__(self):
return 14
assert six.advance_iterator(myitersub()) == 14
def test_iterator():
class myiter(six.Iterator):
def __next__(self):
return 13
assert six.advance_iterator(myiter()) == 13
class myitersub(myiter):
def __next__(self):
return 14
assert six.advance_iterator(myitersub()) == 14
def test_iterator():
class myiter(six.Iterator):
def __next__(self):
return 13
assert six.advance_iterator(myiter()) == 13
class myitersub(myiter):
def __next__(self):
return 14
assert six.advance_iterator(myitersub()) == 14
def take(iterable, n):
"""
Return iterator over last n elements of given iterable.
>>> list(take(range(10), 3))
[0, 1, 2]
See: https://docs.python.org/2/library/itertools.html#itertools.islice
:param iterable iterable: Any iterable, e.g. list, range, ...
:param int n: Number of elements to take
:return: Iterator over last n elements
:rtype: iterator
"""
return itt.islice(iterable, n)
def unique(iterable, key=None):
"""
Return only unique elements in iterable. Potentially high mem. consumption!
>>> list(unique([2,3,1,1,2,4]))
[2, 3, 1, 4]
>>> ''.join(unique('this is a test'))
'this ae'
>>> data = [(1,'a'), (2,'a'), (3,'b')]
>>> list(unique(data, key=lambda t: t[1]))
[(1, 'a'), (3, 'b')]
:param iterable iterable: Any iterable, e.g. list, range, ...
:param key: Function used to compare for equality.
:return: Iterator over unique elements.
:rtype: Iterator
"""
seen = set()
for e in iterable:
k = key(e) if key else e
if k not in seen:
seen.add(k)
yield e
def flatten(iterable):
"""
Return flattened iterable.
>>> list(flatten([(1,2), (3,4,5)]))
[1, 2, 3, 4, 5]
:param iterable iterable:
:return: Iterator over flattened elements of iterable
:rtype: Iterator
"""
return itt.chain(*iterable)
