self.low = low

return MyRangeIterator(self.low, self.high)

def skip(self, to_skip):

return MyRangeIterator(self.low, self.high, to_skip)

class MyRangeIterator(object):

def __init__(self, low, high, skip=None):

self.skip = skip

def __next__(self):

if self.current >= self.high:

raise StopIteration

to_return = self.current

self.current += 1

if self.skip and to_return in self.skip:

return self.__next__()

return to_return

# Problem is fixed by uncommenting these lines

# def __iter__(self):

# return self

my_range = MyRange(0,10)

x = sum(my_range) # x = 45

y = sum(my_range.skip({6,9})) # TypeError: 'MyRangeIterator' object is not iterable

<p>The <code>__iter__</code> method of a class should always return an iterator.</p>

<p>Iterators must implement both <code>__next__</code> and <code>__iter__</code> for Python 3, or both <code>next</code> and <code>__iter__</code> for Python 2. The <code>__iter__</code> method of the iterator must return the iterator object itself.</p>

<p>Iteration in Python relies on this behavior and attempting to iterate over an instance of a class with an incorrect <code>__iter__</code> method can raise a <code>TypeError</code>.

</p>

<p>Make sure the value returned by <code>__iter__</code> implements the full iterator protocol.</p>

<p>In this example, we have implemented our own version of <code>range</code>, extending the normal functionality with the ability to skip some elements by using the <code>skip</code> method. However, the iterator <code>MyRangeIterator</code> does not fully implement the iterator protocol (namely it is missing <code>__iter__</code>).</p>

<p>Iterating over the elements in the range seems to work on the surface, for example the code <code>x = sum(my_range)</code> gives the expected result. However, if we run <code>sum(iter(my_range))</code> we get a <code>TypeError: 'MyRangeIterator' object is not iterable</code>.</p>

<p>If we try to skip some elements using our custom method, for example <code>y = sum(my_range.skip({6,9}))</code>, this also raises a <code>TypeError</code>.</p>

<p>The fix is to implement the <code>__iter__</code> method in <code>MyRangeIterator</code>.</p>

<li>Python Language Reference: <a href="https://docs.python.org/3/reference/datamodel.html#object.__iter__">object.__iter__</a>.</li>

<li>Python Standard Library: <a href="https://docs.python.org/3/library/stdtypes.html#typeiter">Iterator Types</a>.</li>

ClassObject return_type(FunctionObject f) {

ret.getScope() = f.getFunction() and

ret.getValue() = n.getNode() and

from ClassObject iterable, FunctionObject iter, ClassObject iterator

iter = iterable.lookupAttribute("__iter__") and

iterator = return_type(iter) and

not iterator.isIterator()

select iterator,

"Class " + iterator.getName() +

" is returned as an iterator (by $@) but does not fully implement the iterator interface.",

iter, iter.getName()

| protocols.py:98:5:98:33 | Function __getitem__ | Function always raises $@; raise LookupError instead | file://:Compiled Code:0:0:0:0 | builtin-class ZeroDivisionError | builtin-class ZeroDivisionError |

| protocols.py:101:5:101:26 | Function __getattr__ | Function always raises $@; raise AttributeError instead | file://:Compiled Code:0:0:0:0 | builtin-class ZeroDivisionError | builtin-class ZeroDivisionError |

| file://:Compiled Code:0:0:0:0 | builtin-class object | Class object is returned as an iterator (by $@) but does not fully implement the iterator interface. | protocols.py:16:5:16:23 | Function __iter__ | __iter__ |

| protocols.py:20:1:20:26 | class IteratorMissingNext | Class IteratorMissingNext is returned as an iterator (by $@) but does not fully implement the iterator interface. | protocols.py:22:5:22:23 | Function __iter__ | __iter__ |

| protocols.py:20:1:20:26 | class IteratorMissingNext | Class IteratorMissingNext is returned as an iterator (by $@) but does not fully implement the iterator interface. | protocols.py:27:5:27:23 | Function __iter__ | __iter__ |

| protocols.py:30:1:30:26 | class IteratorMissingIter | Class IteratorMissingIter is returned as an iterator (by $@) but does not fully implement the iterator interface. | protocols.py:40:5:40:23 | Function __iter__ | __iter__ |

| protocols.py:54:1:54:29 | class AlmostIterator | Class AlmostIterator is an iterator but its $@ method does not return 'self'. | protocols.py:62:5:62:23 | Function __iter__ | __iter__ |

| protocols.py:74:5:74:22 | Function __del__ | Overly complex '__del__' method. |

| protocols.py:104:1:104:12 | Function f | Too few parameters for special method __add__, which has 1 parameter, but should have 2, in class $@. | protocols.py:107:1:107:29 | class MissingMethods | MissingMethods |

| protocols.py:104:1:104:12 | Function f | Too few parameters for special method __set__, which has 1 parameter, but should have 3, in class $@. | protocols.py:107:1:107:29 | class MissingMethods | MissingMethods |

class IteratorMissingNext:

def __iter__(self):

return self

class IterableMissingNext:

def __iter__(self):

return IteratorMissingNext()

class IteratorMissingIter:

def next(self):

pass

def __next__(self):

pass

class IterableMissingIter:

def __iter__(self):

return IteratorMissingIter()

class IterableWithGenerator:

# returning a generator from __iter__ in an iterable is ok

def __iter__(self):

i = 0

while True:

yield i

i += 1