12/20
2015
Diving In
Iterators are the “secret sauce(n. 酱油；沙司；调味汁)” of Python 3. They’re everywhere, underlying everything, always just out of sight. Comprehensions are just a simple form of iterators. Generators are just a simple form of iterators. A function that yields values is a nice, compact way of building an iterator without building an iterator. Let me show you what I mean by that.
Remember the Fibonacci generator? Here it is as a built-from-scratch iterator:
class Fib:
'''iterator that yields numbers in the Fibonacci sequence'''
def __init__(self, max):
self.max = max
def __iter__(self):
self.a = 0
self.b = 1
return self
def __next__(self):
fib = self.a
if fib > self.max:
raise StopIteration
self.a, self.b = self.b, self.a + self.b
return fib