Very much picking up from the mindset expressed in my earlier post... with the knowledge that this could (and probably should) be broken up into at least three different rants...
I've been working heavily in Python for the past couple of months, regrettably letting some other projects slide a bit. Now done with that, I spent yesterday picking up where I'd left off in a moderately-sized, reasonably well-designed PHP 5.2 project. (Bear in mind that my PHP experience is easily 5 or 6 times as much as my Python.)
Why is this? Three years ago, Joel Spolsky wrote an excellent rant on The Perils of JavaSchools. His point essentially boils down to that how you're trained (or "educated") as a developer shapes the way you look at problems; if all you know is a "Hammer", you try to visualize every problem as a "Nail" (even when it's a "Glass Figurine"). You may well have less-than-satisfying success with that view.
More importantly, the tools and techniques you know shape whether you can properly understand a problem at all. Not having certain features in a language (or not being knowledgeable in their use) means that you'll write clunky, hard-to-understand (and therefore -maintain) code to achieve the desired result...and wind up with (an attempt at) calculus using Roman numerals. Just as having a positional numeric system (e.g. Arabic or "modern" numerals) makes whole classes of problems possible that weren't otherwise, languages and their features make programming problems practical or more efficient.
What we don't want is one language that tries to do everything, in every way possible. We already have that; it's called Perl, and one ramification of its overriding philosophy, "There's more than one way to do it", is that there's always a better way to do it; the search for same can and often does suck in resources faster than a Sol-sized black hole. This also illustrates the failing of most of the more recent practitioners of software development that I've worked with. While those of us who've been working since before oh, about 1988 or 1990 generally make a point of reading at least one new technical book a month, I recently led a group of about 20 young (less than 5 years experience as of 2006) developers where not a single one admitted to reading more than one technical book a year since graduation. These people didn't know how to solve the problem we were working on because the two or three tools which they were familiar with encourage their users to think in ways that do not lead to effective solutions for this problem.
A language, any language, can really only do a limited number of things well. If you are fluent in more than one human language, say, English and Mandarin Chinese, think for a moment about concepts and sayings that are natural in one language but just don't work well in the other. Computer languages are like that, too, which is one reason why your computer's operating system is much less likely to be written in COBOL than your company's accounting program is (with benefits for all concerned).
Getting back to what started this rant....coming back to PHP after a sojourn in Python....
PHP gets the job done. Recent versions, particularly the current 5.2, are much more pleasant to work in than previous versions were for those of us who "think in objects". But it has taken years to get here.
As I look at one class in particular in this PHP project's code base, part of my mind is working on "if this were Python code, I'd write it like..." — and a two-hundred-line unit of code would be about 60 or 80, and much cleaner and easier to understand to boot. Why is that? Think "original intent".
PHP was originally developed as an adjunct to HTML for Web pages, to provide some simple dynamic content. It then "just growed", adding new features and capabilities (database access, object orientation) as it became used in a wider variety of problems. It is, quite simply, a tool that grew into a reasonably useful — if not quite general-purpose — language. There are a number of things it does quite well, especially since it can be used to do useful work without requiring a steep learning curve beforehand.
Python is different. A general-purpose language, with functional-programming features, it is useful for Web application development (e.g., with mod_python for the Apache Web server). Whereas Perl has the idea that "There's more than one way to do it" — and therefore neither a best way, nor strictly an advance certainty that anything in particular will work — Python argues that "there should be one — and preferably only one — obvious way to do it", whatever "it" is.
So am I suggesting that PHP developers ditch everything and go with Python? Of course not. What I am arguing is the seemingly quaint notion that developers, especially those who aspire to work in the craft for a living, should continually strive to learn new tools, techniques, languages and processes. Your abilities are like every other living thing; they're either growing, or they're dying.