My new job involves a lot more PHP, which seems closely related to Perl. There are a number of observations that I would make in the comparison between PHP and Python.

1. PHP is more verbose. In particular, PHP requires braces around code blocks, semi-colons, $ on variable names. Python requires only the colon at the end of certain lines.

2. Both have good libraries. However, the ability of Python to easily interface to shared libraries written in any language, and not specifically written for Python, is a big advantage, in my opinion.

3. PHP has more unexpected gotchas. I hadn’t noticed this when writing in Python (the absence of a problem is less noticeable than the presence of the same problem). One example I came across today:

is_file() tests for the existence of a file, as you would expect by the name. But it is cached. So if you are waiting for a file to disappear, and you repeatedly call is_file to test this, then you will wait for a long time. You need to call clearstatcache() between each call to get an honest answer.

Of course, the documentation states this. But it also states that file_exists (an equivalent function) is also cached. But it appears not to be (PHP v5.3.3):

<?php

print "Waiting for test.txt to appear\n";
while (!is_file("test.txt"))
{
}

print "Waiting for test.txt to disappear\n";
while (True)
{
    sleep(.2);
    if (!is_file("test.txt"))
    {
        print "is_file detected disappearance\n";
        exit(0);
    }
    elseif (!file_exists("test.txt"))
    {
        print "file_exists detected disappearance\n";
        exit(0);
    }
}

?>

Running this code (and creating, then deleting file test.txt) invariably results in the detection by file_exists, even though I have biased it to let is_file test it first.

So ideally you need accurate documentation. But I think even better is to write in a way that requires minimal documentation.