Python iterators and generators

List1 = ITER ([11,22,33,44,55,66,77,88,99])
Print (list1.__next__ ())   
Print (list1.__next__ ())
Results:
11
22
Conclusion: The iterator can only take the next value.

Application:

fp = open ("Ha.bak")
For line in FP:
    Print (Line.strip (' \ n '))
Fp.close ()

With open ("Ha.bak", ' R ') as FP:
    For line1 in FP:
        Print (Line1.strip ())

The for line in FP can also be used for the fp.readlines () function, but it is very inefficient to read, and the for-line in FP can be read into memory like an iterator without a one-time read-in.


Generator:

 def Fab (max): 
 N = 0 
 A = 0 
 B = 1 
 while n < max: 
 yield b  
 #print (b) 
 A, B = B, a + b 
 N = n + 1 
 
 F = Fab (5) 
 Print (F.__next __ ()) 
 Print (f.__next__ ()) 
 Print (f.__next__ ()) 
 Print (f.__next__ ()) 
 Print (f.__next__ ()) 
 Print (f._　_next__ ()) 
 using the yield parameter is equivalent to returning a value (b), but such a return is not returned as the end of the function, but rather as an interruption, the next time you visit, or from that interrupt just before. 

1
1
2
3
5
Traceback (most recent):
File "d:/python/day3/test.py", line A, in <module>
Print (f.__next__ ())
Stopiteration

See another example "

Def withdraw (account):
    While account > 0:
        Account-= 100
        Yield 100
        Print ("Withdraw again")

F = Withdraw (500)
Print (f.__next__ ())
Print (f.__next__ ())

Print (f.__next__ ())

Print (f.__next__ ())

Print (f.__next__ ())
Print (f.__next__ ())

100
Withdraw again
100
Withdraw again
100
Withdraw again
100
Withdraw again
100
Withdraw again
Traceback (most recent):
File "d:/python/day3/test.py", line +, in <module>
Print (f.__next__ ())
Stopiteration

In this example, a maximum of 100 can be taken at most five of the time to withdraw money. You can add other program code in the middle of the print (f.__next__ ()) function, and when the iterator comes back to run, it starts with the state you just saved. Such a function of producing iterators is called generators.

Python iterators and generators