python iterator

#Objects with the __next__ method are considered to be iterable and can be iterated through x.__next__(). When iterating to an empty line, an error will be reported StopIteration
 f= open ( 'e:/kangujiao/test.txt' )
 print ( iter (f) is f)      #The file itself is an iterator
 print (f. __next__ (), end = '' )
 print (f. __next__ (), end = '' )
 #print(f. __next__(),end ='')
 #Built-in function next, it will automatically use the __next__ method of the object. Given an iterable object, calling next(x) is the same as x.__next__(), and an error will be reported when iterating to an empty line StopIteration
 f= open ( 'e:/kangyuujiao/test.txt' )
 print ( next
(f), end = '' )
 print ( next (f), end = '' )
 #print(next(f),
 end='') #When the for loop starts, it will be passed to the iter built-in function, In order to get an iterator from an iterable object, the returned object contains the required next method
 l=[ 1 , 2 , 3 ]
 print ( iter (l) is l)    #list is not an iterator
 i= iter (l)
 print ( i. __next__ ())
 print (i. __next__ ())
 print (i. __next__ ())

#Other iteration environments
 print ( sum ([ 1 , 2 , 3 , 4 , 5 ]))     #15
 print ( list ( open ( 'e:/kangujiao/test.txt' )))    #returns the lines in the file consisting of List
 print ( tuple ( open ( 'e:/kangyujiao/test.txt' )))    #return a tuple of lines in the file
 print ( '&&' .join( open ( 'e:/kangyujiao/test.txt' )))    #returns a string of lines in the file
 a,b,c,d= open ('e:/kangyuujiao/test.txt' )   #The lines in the file are assigned to a,b,c,d
 print (a,b,c,d)
a,*b= open ( 'e:/kangyujiao/test.txt' )   #The first line in the file is assigned to a, and the others are assigned to b
 print (a,b)
 print ( set ( open ( 'e:/kangyujiao /test.txt ' )     )) #return the set of lines in the file
 print ({i:j for i,j in enumerate ( open ( 'e:/kangyujiao/test.txt' ))})    #return to the file A dictionary of lines

#Multiple iterators vs a single iterator#
 range itself is not an iterator. After an iterator is generated, it supports multiple iterators, and these iterators will remember their respective positions
 r= range ( 3 )
i1= iter (r)
 print ( next (i1))    #0
 print ( next (i1))    #1
 i2= iter (r)
 print ( next (i2))    #0
 print ( next (i2))    #1
 #zip , map and filter do not support multiple active iterators on the same result
 z= zip (( 1 , 2 , 3 ),( 4 , 5 , 6 ))

i1=iter(z)
i2=iter(z)
print(next(i1))     #(1,4)
print(next(i1))     #(2,5)
print(next(i1))     #(3,6)

z=map(abs, (-1,-2,-3,-4))
i1=iter(z)
i2=iter(z)
print(next(i1))     #1
print(next(i1))     #2
print(next(i1))     #3