How to understand Python iterators and generators?

SXXpenguin 2020-11-06 20:07:16
understand python iterators generators


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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