CODEWITHSUNDEEP
pythonbuilt-in
M.Taki_Eddine
M.Taki_Eddine

Reputation: 160

About the built-in __iter__

I'm learning python and reading fluent python book! While following some class implementation, I stopped by this snippet of code:

def __iter__(self):
    return iter(self._components)

with components being an array of floats, my question is: why calling the iter() method on components although it's already an iterable?.

Upvotes: 0

Views: 72

Answers (1)

Antti Haapala -- Слава Україні
Antti Haapala -- Слава Україні

Reputation: 133988

While the documentation doesn't make it very clear, it is because __iter__ must (not should) return an iterator, not an iterable:

% python
Python 3.6.3 (default, Oct  3 2017, 21:45:48) 
[GCC 7.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> class Foo:
...     def __iter__(self):
...         return []
... 
>>> iter(Foo())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: iter() returned non-iterator of type 'list'

Upvotes: 3

Related Questions