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How to understand Python iterators and generators?

2020-11-06 20:07:16 SXXpenguin

   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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