How can I use .htaccess to hide .php URL extensions?

I want something to put in my .htaccess file that will hide the .php file extension for my php files, so going to www.example.com/dir/somepage would show them www.example.com/dir/somepage.php.

Is there any working solution for this? My site uses HTTPS, if that matters at all.

This is my .htaccess at the moment:

RewriteEngine On

RewriteCond %{SERVER_PORT} 80 
RewriteRule ^(.*)$ https://www.example.com/$1 [R,L]

ErrorDocument 404 /error/404.php

RewriteCond %{REQUEST_FILENAME}.php -f
RewriteCond %{REQUEST_URI} !/$
RewriteRule (.*) $1\.php [L]