Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Many answers come close to the point but miss it.</p> <p>An <strong><code>Iterator</code></strong> is an object that is consumed by iterating over it. There is no way around it. Example of iterator objects are those returned by calls to <a href="http://docs.python.org/2/library/functions.html#iter" rel="nofollow"><code>iter()</code></a>, or those returned by the functions in the <a href="http://docs.python.org/2/library/itertools.html" rel="nofollow"><code>itertools</code> module</a>.</p> <p>The proper way to check whether an object is an iterator is to call <code>isinstance(obj, Iterator)</code>. This basically checks whether the object implements the <code>next()</code> method (<code>__next__()</code> in Python 3) but you don't need to care about this.</p> <p>So, remember, an iterator is always consumed. For example:</p> <pre><code># suppose you have a list my_list = [10, 20, 30] # and build an iterator on the list my_iterator = iter(my_list) # iterate the first time over the object for x in my_iterator: print x # then again for x in my_iterator: print x </code></pre> <p>This will print the content of the list just <strong>once</strong>.</p> <p>Then there are <code>Iterable</code> objects. When you call <code>iter()</code> on an iterable it will return an iterator. Commenting in this page I made myself an error, so I will clarify here. Iterable objects are not required to return a <em>new iterator</em> on every call. Many iterators themselves are iterables (i.e. you can call <code>iter()</code> on them) and they will return the object itself.</p> <p>A simple example for this are list iterators. <code>iter(my_list)</code> and <code>iter(iter(my_list))</code> are the same object, and this is basically what @glglgl answer is checking for.</p> <p>The <a href="http://docs.python.org/2/library/stdtypes.html#iterator-types" rel="nofollow">iterator protocol</a> requires iterator objects to return themselves as their own iterator (and thus be iterable). This is not required for the iteration mechanics to work, but you wouldn't be able to loop over the iterator object.</p> <p>All of this said, what you should do is check whether you're given an Iterator, and if that's the case, make a copy of the result of the iteration (with <code>list()</code>). Your <code>isconsumable(obj)</code> is (as someone already said) <code>isinstance(obj, Iterator)</code>.</p> <p>Note that this also works for <code>xrange()</code>. <code>xrange(10)</code> returns an <code>xrange</code> object. Every time you iter over the xrange objects it returns a new iterator starting from the start, so you're fine and don't need to make a copy.</p>
    singulars
    1. This table or related slice is empty.
    1. PODetecting if an iterator will be consumed
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USDavide R.
    1. USDavide R.
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CONormally, an iterator should be an iterable as well and thus return `self` from its `__iter__()` in order to iterate over it as well and not only its "parent". See http://docs.python.org/2/library/stdtypes.html#iterator.__iter__. Otherwise you couldn't do `it = iter(l); for i in it: ...`. Till now, I never came across Iterators which weren't iterable as well.
      singulars
      1. PO
      1. USglglgl
    2. COYou're right, thank you again. I will fix the answer.
      singulars
      1. PO
      1. USDavide R.
    3. CO@glglgl so basically your answer works fine in all cases that implement the iterator protocol as described in the docs you linked. The identity check baffles me, but it will indeed work. Again, sorry for making a wrong point without checking the right docs.
      singulars
      1. PO
      1. USDavide R.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload