Python len() method not returning value : <p>I have started learning python programming language and learning string in python. </p>

<p>i am using following code to find the length of string.</p>

<pre><code>a = "Hello, World!"
print(a.len())
</code></pre>

<p>but code is not working. I know i am using method len after variable. But why other method works after variable? E.G print(a.lower()) to lower sting, print(a.upper()) to upper string </p>
