Well, We created a very simple custom module that will override the core product listing block (app/code/core/Mage/Catalog/Block/Category/View.php) in the category known as page view.

Our first step should be to create one module file. Create a file ‘app/etc/modules/Namespace_Catalog.xml’ and paste the below content into that file:

<?xml version="1.0"?>
<config>
  <modules>
    <Namespace_Catalog>
      <active>true</active>
      <codePool>local</codePool>
    </Namespace_Catalog>
  </modules>
</config>

Next, we have to create a module configuration file. Create “app/code/local/Namespace/Catalog/etc/config.xml” and paste the below contents in that file.

<?xml version="1.0"?>
<config>
  <modules>
    <Namespace_Catalog>
      <version>1.0</version>
    </Namespace_Catalog>
  </modules>
 
  <global>
    <blocks>
      <catalog>
        <rewrite>
          <category_view>Namespace_Catalog_Block_Category_View</category_view>
        </rewrite>
      </catalog>
    </blocks>
  </global>
</config>

At the starting point of module, we’ve done a set-up of the module’s version no. by using <version> tag. Following to it, the <catalog> and <rewrite> tags are utilized to override. So Magento system knows that we’re going to override one of the “blocks” of the “Catalog” core module.

The <category_view> tag is utilized to define the identity of the block and that will be overridden by the Namespace_Catalog_Block_Category_View class. It’s mapped to a block file “Category/View.php” under the “Block” directory of the Catalog module.

The last step will be to define a block class Namespace_Catalog_Block_Category_View. Let’s create a block file “app/code/local/Namespace/Catalog/Block/Category/View.php” and paste the below code in that file:

<?php
class Namespace_Catalog_Block_Category_View extends Mage_Catalog_Block_Category_View
{
  public function getProductListHtml()
  {
    /** Your Custom Code Goes Here **/
    return $this­>getChildHtml('product_list');
  }
}

We have defined the Namespace_Catalog_Block_Category_View class which extends the core Mage_Catalog_Block_Category_View block class. Thus, you can easily override the method of the base class and create new methods when required.