0 Basic python-13.2 Manual iterations: ITER and Next

Let's talk about this chapter. Manual iterations: ITER and Next

1.next

We've already mentioned this next in the last section, and we're going to expand it here, outside of the __next__ () method, we can also use the built-in function next (file) to implement

Here are the two sets of code listings with the same functionality:

>>> handler=open (' output_file.txt ') >>> next (handler) ' aaaaa\n ' >>> Next (handler) ' Bbbbb\ N ' >>> Next (handler) ' ccccc\n ' >>> Next (handler) ' ddddd\n ' >>> Next (handler) ' Fffff ' >> > Next (Handler) Traceback (most recent):  File "<pyshell#6>", line 1, in <module>    next ( Handler) stopiteration>>> Handler.close ()

>>> handler=open (' output_file.txt ') >>> handler.__next__ () ' aaaaa\n ' >>> handler.__next__ () ' bbbbb\n ' >>> handler.__next__ () ' ccccc\n ' >>> handler.__next__ () ' ddddd\n ' >>> handler._ _next__ () ' Fffff ' >>> handler.__next__ () Traceback (most recent call last):  File "<pyshell#14>", line 1, in <module>    

Both sets of code implement the same function: The next line of the file is read, and the end of the two methods is the end of a catch stopiteration exception

2.iter

ITER is an iterator. Let's first cite an example:

>>> alist=[1,2,3]>>> iter=iter (alist) >>> iter.__next__ () 1>>> Next (Iter) 2

The above steps are:

1) Create a list

2) returns an iterator via the ITER () method

3) Call the __next__ method of the iterator, or use the built-in function next () to get the contents of the next

Now the question is, why does the above file iterator not use ITER?

Let's proceed to the above code to get the following example:

Through the is test we see that the list returns an iterator only after calling the ITER () function, and for the file, the open itself returns an iterator.

So, for the return of a file, it returns a file iterator

For a list of iterations, we summarize the following two methods:

3. Other built-in types of iterators

1) Range

Although the above two methods, but we still recommend the use of the following one, more convenient and concise

2) Dictionary

>>> for key in Adict.keys ():p rint (Key,adict[key]) C 3b 2a 1

>>> adict={' A ': 1, ' B ': 2, ' C ':3}>>> for key in Adict:print (Key,adict[key]) C 3b 2a 1

Through the comparison of the above methods, we recommend the use of the last one, concise and clear

Summary: This chapter focuses on the use of the ITER iterator and next, as well as examples of their applications in lists, files, dictionaries, and other built-in types.

This chapter is here, thank you.

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0 Basic python-13.2 Manual iterations: ITER and Next