One of the key technologies sought by web developers is a unified and modular way to incorporate business logic into the presentation layer of a web page. While it is simultaneously important to maintain a useful separation of data and presentation, it has always been the goal of developers to integrate the programming with the data as closely as possible to avoid unusual bugs and improve reliability. This, among other reasons, is why PHP is so popular.
Server to Client
From a technical standpoint, PHP is a preprocessor, or logic that executes in the rendering step just prior to the markup language in a web page being evaluated. It is a very powerful way to add logic to a site, because the program instructions run in the server’s memory and namespace while the data and presentation layer run in the client’s memory and namespace. This has two effects. One, it means client-side manipulation can’t affect the server-side data or logic and two, it means the client can process data independently of the server’s code.
PHP is tightly integrated with the HTTP protocol, meaning it can take input from both POST and GET operations, set cookies and gather user input from both forms and direct variable assignments and then process that information server-side before forming it as HTML output and re-presenting it back to the user. One important reason this is possible is because PHP is interpreted and managed by the web server software itself as opposed to a completely separate interpreter.
Comparison with Python and Ruby
Two other popular web development frameworks are Python and Ruby. Python is a standalone scripting language that shares a lineage with the Common Gateway Interface languages like Perl and C. Python and Ruby both share many different web frameworks and Python in particular is at least as popular if not more popular than PHP itself. Python is more scalable than either Ruby or PHP. Ruby is a faster language to start a project with, but is more difficult to manage in large-scale applications.
One major advantage Python has over most web languages is its origin as a standalone scripting language. It is very popular as a bolt-on interpreter for other software packages and for this reason is highly versatile. PHP and Ruby, meanwhile, are more optimized for web frameworks and web applications and are therefore a little tougher to adapt to unusual situations. So, is PHP better than Python? Or Ruby?
As with all computer languages, some are better at certain tasks than others. The key to building a good application is knowing the difference and using the right tool for the job at hand.