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Generator Functions

The iter function can be used to acquire an iterator object associated with a container like a sequence, set, file or dict. We can then manipulate this iterator explicitly to handle some common situations.

iter( iterable ) → iterator

Returns the iterator from an object. This iterator interacts with built-in types in obvious ways. For sequences this will return each element in order. For sets, it will return each element in no particular order. For dictionaries, it will return the keys in no particular order. For files, it will return each line in order.

Gettimg an explicit iterator — outside a for statement — is very handy for dealing with data structures (like files) which have a head-body structure. In this case, there are one or more elements (the head) which are processed one way and the remaining elements (the body) which are processed another way.

We'll return to this in detail in Chapter 19, Files . For now, here's a small example.

>>> 
seq=range(10)

>>> 
seqIter= iter(seq)

>>> 
seqIter.next()

0
>>> 
seqIter.next()

1
>>> 
for v in seqIter:
...     print v



2
3
4
5
6
7
8
9

1

We create a sequence, seq. Any iterable object would work here; any sequence, set, dict or file.

2

We create the iterator for this sequence, and assign it to seqIter. This object has a next method which is used by the for statement. We can call this explicitly to get past the heading items in the sequence.

3

Here, we call next explicitly to yield the first two elements of the iterator.

4

Here, we provide the iterator to the for statement. The for statement repeatedly calls the next method and executes its suite of statements.


 
 
  Published under the terms of the Open Publication License Design by Interspire