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magic methods 7

admin 11月 12, 2020 0

BIF : iter()、next()

We can use this two BIF to realize the function of for statement.

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>>> for each in "ABCDE":
	print(each)

	
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The before with for can be realized with the two BIF and while statement in below.

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>>> string = "ABCDE"
>>> it = iter(string)
>>> while True:
	try:
		each = next(it)
	except StopIteration:
		break
	print(each)

	
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The magic methods of two BIF is __iter__() and __next__(). The returned value of the former is itself while the latter dominates the rule of the iteration.

Try with Fibonacci sequence.

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class Fibs:
	def __init__(self):
		self.a = 0
		self.b = 1
	def __iter__(self):
		return self
	def __next__(self):
		self.a, self.b = self.b, self.a + self.b
		return self.a
# Pay attention to the limit!
>>> fibs = Fibs()
>>> for each in fibs:
	if each < 1000:
		print(each)
	else:
		break

	
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987

We can add a parameter to control the iteration.

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class Fibs:
	def __init__(self, n=10):
		self.a = 0
		self.b = 1
		self.n = n
	def __iter__(self):
		return self
	def __next__(self):
		self.a, self.b = self.b, self.a + self.b
		if self.a > self.n
			raise StopIteration
		return self.a
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