How to understand Python iterators and generators?

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　　 How to understand Python Iterators and generators ? stay Python in , Use for ... in ... It can be done to list、tuple、set and dict Data types are iterated , You can filter out all the data . as follows ：

　　for element in [1, 2, 3]:

　　print(element)

　　for element in (1, 2, 3):

　　print(element)

　　for key in {'one':1, 'two':2}:

　　print(key)

　　for char in "123":

　　print(char)

　　for line in open("myfile.txt"):

　　print(line, end='')

　　1、 iterator

　　 The string , list , Use built-in functions iter Convert to an iteratable object , Use next keyword , Iteratable objects take one value at a time . Like the following code ：

　　nums = [1,2,3,4]

　　nums = iter(nums)

　　print(next(nums))

　　print(next(nums))

　　print(next(nums))

　　print(next(nums))

　　 Output

　　1

　　2

　　3

　　4

　　 If it exceeds the length of the data , Will be an error StopIteration

　　nums = [1,2,3,4]

　　nums = iter(nums)

　　print(next(nums))

　　print(next(nums))

　　print(next(nums))

　　print(next(nums))

　　print(next(nums)) # Over data length , Report errors StopIteration

　　2、 generator

　　 Using generators, you can create iterators . The generator mainly uses yeild keyword , Every time you call next When it comes to yeild The definition of the corresponding . for example ： We need to take 10～20 Data between , In steps of 2, You can use the following code

　　for x in range(10,20,2):

　　print(x)

　　 But if the step size is set to 0.5, The following code ：

　　for x in range(10,20,0.5):

　　print(x)

　　 Will be an error

　　TypeError: 'float' object cannot be interpreted as an integer

　　 This is the time , We can use The generator comes from defining a function

　　def drange(start,stop,step):

　　x = start

　　while x< stop:

　　yield x

　　x += step

　　for x in drange(10,20,0.5):

　　print(x)

　　 Another example ：

　　 Given a string , Flashback to arrange ：

　　def reverse(data):

　　for x in range(len(data)-1,-1,-1):

　　yield data[x]

　　for x in reverse('gold'):

　　print(x)

　　 See here , I believe that we can understand Python Iterators and generators have a certain understanding . More about dry goods , In the erudite Valley IT Training platform , From zero basis to advanced promotion, the learning content of each stage of learning is waiting for you !

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