Python iterator and Generator

Python iterator and Generator

I. iterators
The iterator is only a container object and implements the iterator protocol. It has two basic methods:
1) Next Method
Returns the next element of the container.
2) _ ITER _ Method
Return iterator itself

The iterator can be created using the built-in ITER method. See the example below:
>>> I = ITER ('abc ')
>>> I. Next ()
'A'
>>> I. Next ()
'B'
>>> I. Next ()
'C'
>>> I. Next ()
Traceback (most recent call last ):
File "<string>", line 1, in <string>
Stopiteration:

Class myiterator (object ):
Def _ init _ (self, step ):
Self. Step = step
Def next (Self ):
"Returns the next element ."""
If self. Step = 0:
Raise stopiteration
Self. Step-= 1
Return self. Step
Def _ ITER _ (Self ):
"Returns the iterator itself ."""
Return self
For El in myiterator (4 ):
Print el
--------------------
Result:
3
2
1
0

Ii. Generators
Since python2.2, the generator provides a simple way to help return functions of list elements to complete simple and effective functions.Code.
It allows you to stop a function and return results immediately based on the yield command.
This function saves the execution context. If necessary, you can continue execution immediately.
For example, the Fibonacci function:
Def maid ():
A, B = 0, 1
While true:
Yield B
A, B = B, A + B
FIB = maid ()
Print fib. Next ()
Print fib. Next ()
Print fib. Next ()
Print [fib. Next () For I in range (10)]
--------------------
Result:
1
1
2
[3, 5, 8, 13, 21, 34,55, 89,144,233]

Pep Python enhancement proposal Python enhancement suggestions

Tokenize Module
>>> Import tokenize
>>> Reader = open ('C:/temp/py1.py'). Next
>>> Tokens = tokenize. generate_tokens (Reader)
>>> Tokens. Next ()
(1, 'class', (1, 0), (1, 5), 'class myiterator (object):/N ')
>>> Tokens. Next ()
(1, 'myiterator', (1, 6), (1, 16), 'class myiterator (object):/N ')
>>> Tokens. Next ()
(51, '(', (1, 16), (1, 17), 'class myiterator (object):/N ')

Example:
Def power (values ):
For value in values:
Print 'powering % s' % value
Yield Value
Def adder (values ):
For value in values:
Print 'adding to % s' % value
If Value % 2 = 0:
Yield Value + 3
Else:
Yield Value + 2
Elements = [,]
Res = adder (Power (elements ))
Print res. Next ()
Print res. Next ()
--------------------
Result:
Powering 1
Adding to 1
3
Powering 4
Adding to 4
7

Keep code simple, not data.
Note: You would rather have a large number of simple iteratable functions than a complex function that calculates only one value at a time.

Example:
Def psychologist ():
Print 'Please tell me your problems'
While true:
Answer = (yield)
If answer is not none:
If answer. endswith ('? '):
Print ("don't ask yourself too much questions ")
Elif 'good' in answer:
Print "A That's good, go on"
Elif 'bad' in answer:
Print "Don't be so negative"
Free = psychologist ()
Print free. Next ()
Print free. Send ('I Feel Bad ')
Print free. Send ("why I shouldn't? ")
Print free. Send ("OK then I shocould find what is good for me ")
--------------------
Result:
Please tell me your problems
None
Don't be so negative
None
Don't ask yourself too much questions
None
A That's good, go on
None