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<br>

<h3>Python Iterators</h3>

<hr>

<p>An <b>iterator</b> may be defined as an object that contains countable number of values.<br>

In other words an <b>iterator</b>is an object through which we can traverse all the given values.<br>

In python, techically an <b>iterator</b> is an object which consists of <b>__iter__()</b> and <b>__next__()</b> methods.</p>

<h5>The iter() method</h5>

<p>As we know, list,tuples,dictionaries,sets are iterable objects.All these objects have their <b>iter()</b> method which is used to get an iterator.<br>Lwt's take an example of a <b>list</b>.</p>

<b>Example:</b>

<pre><code>list1 = ["january", "february", "march"]

iterator1 = iter(list1)

print(next(iterator1))

</code></pre>

<b>Output:</b>

<pre><code>january

february

march

</code></pre>

<p>In the above code, we create a list named <b>list1</b> in which we used <b>iter()</b> method to access all the elements.</p>

<p><b>Note:</b>Strings are also iterable objects.It will work same as list worked above.</p>

<h5>Using loop through an Iterator</h5>

<p>We can also use loop to iterate through the iterable objects.<br>

For example,take <b>for</b> loop in to iterate through objects.</p>

<b>Example:</b>

<pre><code>list1 = ["january", "february", "march"]

for var in list1:

print(var)

</code></pre>

<b>Output:</b>

<pre><code>january

february

march</code></pre>

<p>We can also use loops in tuple,dictionaries ,sets as well as strings.</p>

<h5>Creation of Iterators</h5>

<p>For craetion of an <b>bject/class</b> as an iterator, we have to use 2 methods here:</p>

<p>The above methods should be implemented to the objects.</p>

<p><b>__iter__() method-</b> This method is helps us to perform the operations but it will always return the iterator object itself.</p><br>

<p><b>__next__() method-</b> This method allows us to do operations and it will return the next item in the sequence.</p><br>

<b>Example:</b>

<pre><code>class Multiple:

def __iter__(self):

self.num = 10

return self

def __next__(self):

var = self.num

self.num *= 10

return var

nclass = Multiple()

iterator = iter(nclass)

print(next(iterator))

</code></pre>

<b>Output:</b>

<pre><code>10

100

1000

10000

100000

</code></pre>

<h5>StopIteration statement</h5>

<p>This statement is used to stop the iteration at a particular condition. It will prevent the iteration to go on forever.<br>

In the __next__() method, we can add a terminating condition to raise an error if the iteration is done a specified number of times.<br></p>

<b>Syntax:</b>

<pre><code>def __next__(self):

if <b>condition</b>:

code

else:

raise <b>StopIteration</b> #The <b>raise</b> keyword is used to raise an exception.

</code></pre>

<b>Example:</b>

<pre><code>class Multiple:

def __iter__(self):

self.num = 10

return self

def __next__(self):

if self.num <=100000: #condition

var = self.num

self.num *= 10

return var

else:

raise <b>StopIteration</b>

numclass = Multiple()

iterator = iter(numclass)

for var in iterator:

print(var)

</code></pre>

<b>Output:</b>

<pre><code>10

100

1000

10000

100000

1000000

</code></pre>

<p>In the above code, we used the statement <b>StopIteration</b> to prevent our loop to run forever.</p>

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