I have the following code in django.template:
class Template(object):
def __init__(self, template_string, origin=None, name='<Unknown Template>'):
try:
template_string = smart_unicode(template_string)
except UnicodeDecodeError:
raise TemplateEncodingError("Templates can only be constructed from unicode or UTF-8 strings.")
if settings.TEMPLATE_DEBUG and origin is None:
origin = StringOrigin(template_string)
self.nodelist = compile_string(template_string, origin)
self.name = name
def __iter__(self):
for node in self.nodelist:
for subnode in node:
yield subnode
def render(self, context):
"Display stage -- can be called many times"
return self.nodelist.render(context)
The part I am confused about is below. How does this __iter__
method work? I can't find any corresponding next
method.
def __iter__(self):
for node in self.nodelist:
for subnode in node:
yield subnode
This is the only way that I know how to implement __iter__
:
class a(object):
def __init__(self,x=10):
self.x = x
def __iter__(self):
return self
def next(self):
if self.x > 0:
self.x-=1
return self.x
else:
raise StopIteration
ainst = a()
for item in aisnt:
print item
In your answers, try to use code examples rather than text, because my English is not very good.
From the docs :
If a container object's
__iter__()
method is implemented as a generator, it will automatically return an iterator object (technically, a generator object) supplying the__iter__()
and__next__()
methods.
Here is your provided example using a generator:
class A():
def __init__(self, x=10):
self.x = x
def __iter__(self):
for i in reversed(range(self.x)):
yield i
a = A()
for item in a:
print(item)
That __iter__
method returns a python generator (see the documentation ), as it uses the yield
keyword. The generator will provide the next() method automatically; quoting the documentation:
What makes generators so compact is that the __iter__() and next() methods are created automatically.
EDIT:
Generators are really useful. If you are not familiar with them, I suggest you readup on them, and play around with some test code.
Here is some more info on iterators and generators from StackOverflow .
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