In order for instances of Python classes to be iterated, the __iter__ method needs to be implemented. There are three specific ways: 1. Implement __iter__ to return built-in iterators, such as return iter(self.items); 2. Customize the iterator class, implement the __iter__ and __next__ methods at the same time, and ensure that each call __iter__ returns a new instance to support multiple iterations; 3. Use generator functions to simplify the code and use yield in __iter__ to automatically generate iteration logic. If you want the object to iterate multiple times, __iter__ must return a new iterator instead of itself.
In Python, if you want an instance of a class to be iterated (such as traversing with for loop), you need to make it an iterable object. This is not difficult, but there are several key points to pay attention to.
Implement the __iter__ method
The most basic way to make your class iterable is to implement the __iter__ method. This method should return an iterator object , that is, the object that implements the __next__ method.
To give a simple example, if you have a class that stores data, and hope to directly traverse the data in it by using the for item in obj:
class MyCollection:
def __init__(self, items):
self.items = items
def __iter__(self):
return iter(self.items) After writing this way, you can directly iterate on the instance of MyCollection :
c = MyCollection([1, 2, 3])
for x in c:
print(x)Note: In the example above, we used Python's built-in
iter()function to quickly turnself.items(a list) into an iterator. If you want more flexibility in controlling the traversal logic, you can also define an iterator class yourself and return it.
Implement an iterator yourself (optional)
If you don't want to rely on iterators with built-in types (such as lists), but want to completely customize the iteration process, you can implement both __iter__ and __next__ methods in your class. However, at this time your class itself becomes an iterator and can only be traversed once, unless you return a new iterator in __iter__ every time.
For example:
class MyCounter:
def __init__(self, start, end):
self.current = start
self.end = end
def __iter__(self):
return MyCounter(self.current, self.end)
def __next__(self):
if self.current > self.end:
raise StopIteration
value = self.current
self.current = 1
Return value This way you can iterate through the same object multiple times, because each call to __iter__ returns a brand new iterator instance.
Simplify code with generator (recommended)
There is also a simpler way: use yield in the __iter__ method to return a generator function, so that there is no need to define the __next__ method separately.
class MyRange:
def __init__(self, start, end):
self.start = start
self.end = end
def __iter__(self):
current = self.start
While current <= self.end:
yield current
current = 1This method is clearer and easier to maintain.
Basically that's it. As long as you implement __iter__ well and make sure it returns a valid iterator, your class can support iterative operations. Not complicated but easy to ignore is that if you want an object to be iterated multiple times, its __iter__ should return a new iterator every time, not self .
The above is the detailed content of How to make a Python class iterable?. For more information, please follow other related articles on the PHP Chinese website!
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