*Memos:
- My post explains an iterator (1).
- My post explains an iterator (2) and copy.
- My post explains a generator.
You can create a class-based iterator with __iter__() and/or __next__() as shown below:
*Memos:
- Basically,
__iter__()is used to return an iterator. - Basically,
__next__()is used to return the next element.
<iter() & next()>
class Cls: data = ['a', 'b', 'c'] index = 0 def __iter__(self): return self def __next__(self): if self.index < len(self.data): i = self.index self.index += 1 return self.data[i] raise StopIteration v = Cls() print(v) # <__main__.Cls object at 0x000001FCD688B350> # It gets an element but it's not necessary for # a `for` statement, `__next__()` and `next()`. v = v.__iter__() print(v) # <__main__.Cls object at 0x000001FCD688B350> # It gets an element but it's not necessary for # a `for` statement, `__next__()` and `next()`. v = iter(v) print(v) # <__main__.Cls object at 0x000001FCD688B350> for x in v: print(x) # a # b # c v = Cls() print(v.__next__()) # a print(v.__next__()) # b print(v.__next__()) # c print(v.__next__()) # StopIteration: v = Cls() print(next(v)) # a print(next(v)) # b print(next(v)) # c print(next(v)) # StopIteration: <next()>
class Cls: data = ['a', 'b', 'c'] index = 0 def __next__(self): if self.index < len(self.data): i = self.index self.index += 1 return self.data[i] raise StopIteration v = Cls() print(v) # <__main__.Cls object at 0x000001FCD8360440> # v = v.__iter__() # AttributeError: 'Cls' object has no attribute '__iter__' # v = iter(v) # TypeError: 'Cls' object is not iterable # for x in v: # TypeError: 'Cls' object is not iterable # print(x) print(v.__next__()) # a print(v.__next__()) # b print(v.__next__()) # c print(v.__next__()) # StopIteration: v = Cls() print(next(v)) # a print(next(v)) # b print(next(v)) # c print(next(v)) # StopIteration: *__next__() can be the generator with one or more yield statement.
class Cls: data = ['a', 'b', 'c'] index = 0 def __next__(self): if self.index < len(self.data): i = self.index self.index += 1 yield self.data[i] # yield from self.data[i] raise StopIteration v = Cls() print(v) # <__main__.Cls object at 0x000001FCD2EE4E60> print(v.__next__().__next__()) # a print(v.__next__().__next__()) # b print(v.__next__().__next__()) # c print(v.__next__().__next__()) # RuntimeError: generator raised StopIteration v = Cls() print(next(next(v))) # a print(next(next(v))) # b print(next(next(v))) # c print(next(next(v))) # RuntimeError: generator raised StopIteration <iter()>
class Cls: data = ['a', 'b', 'c'] index = 0 def __iter__(self): return self v = Cls() print(v) # <__main__.Cls object at 0x000001FCD6888F80> v = v.__iter__() # It gets an element but it's not necessary. print(v) # <__main__.Cls object at 0x000001FCD6888F80> # v = iter(v) # TypeError: iter() returned non-iterator of type 'Cls' # for x in v: # TypeError: iter() returned non-iterator of type 'Cls' # print(x) # print(v.__next__()) # AttributeError: 'Cls' object has no attribute '__next__' # print(next(v)) # TypeError: 'Cls' object is not an iterator *__iter__() can be the normal function which returns 'Hello'.
class Cls: def __iter__(self): return 'Hello' v = Cls() print(v) # <__main__.Cls object at 0x000001FCD2EE4E60> v = v.__iter__() # It gets an element to print. print(v) # Hello v = Cls() v = iter(v) # TypeError: iter() returned non-iterator of type 'list' *__iter__() can be the generator with one or more yield statement.
class Cls: def __iter__(self): return iter(['a', 'b', 'c']) # def __iter__(self): # It's a generator. # yield 'a' # It gets the same result. # yield 'b' # yield 'c' # def __iter__(self): # It's a generator. # yield from ['a', 'b', 'c'] # It gets the same result. v = Cls() print(v) # <__main__.cls object at 0x000001FCD1A14E60> # It gets an element but it's not necessary for a `for` statement. v = v.__iter__() print(v) # <list_iterator object at 0x000001FCD1C42EF0> for x in v: print(x) v = Cls() v = v.__iter__() # It gets an element for `__next__()`. print(v.__next__()) # a print(v.__next__()) # b print(v.__next__()) # c print(v.__next__()) # StopIteration: v = Cls() v = iter(v) # It gets an element for `next()`. print(next(v)) # a print(next(v)) # b print(next(v)) # c print(next(v)) # StopIteration: 
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