Even if pyhton is installed it isn't certain if it is v.2 or 3.
Neither bash nor python seem to be preinstalled on BSDs.
We had to install it for a code review tool I built.
But despite Bash's weird syntax, I love how we can do very complex tasks within a few lines.
You have one tool that you know well. I have thousands of tools that I've learned daily and I wrap with a bash script..except when I need python/tcl or C. Most of what I do in python/tcl/C is truly complicated, needs to be fast or use a data structure other than an array: as it should be. Most of what I do in the shell is as simple as the userspace tools and bash will let it be. Write the one liner above in python without importing a library.
I think most people are spoiled by being able to install anything; I work in a locked down environment and getting anything non-sanctioned in is very difficult, and the sanctioning process is tedious if nothing else.
That, and the fact that libraries are evolving- which is why we end up with horrible things like package/library version pinning.
For instance the "os" module has an "urandom" function that does essentially the same as the "dd" in the bash script. Of course you could also read from the device so you wouldn't need to import "os". You would need to import "random" to get access to the random number generator, though, but it's still part of the standard library.
> python -c "for i in range(4): print(__import__('os').urandom(12)[__import__('random').randint(1,4):12])"
Or something like it, that bash one liner is pretty unreadable and full of side effects that may or may not be needed. A small 3 line python file would be cleaner and more readable.
This can break quite fast if you rely on something from Bash 4 (released 11 years ago, still not on OS X by default), or some command-line tools that's either not installed or uses switches/functions only available in their GNU incarnations.
For anything that involves more than one file or with a line count going into triple digits, I wouldn't recommend bash. And heck, for those kind of scripts, I'd go one step further and stick with plain 'sh', just to be really sure. Bash adds little. GNU missed the train of transitioning to something like ksh93, probably because RMS thought that everyone would be using Guile once Hurd is out. (I once worked with a pretty large piece of software for packaking/administration mostly written in ksh93, as this was more palatable for commercial Unix users -- not as important these days where you won't run into AIX, HP-UX and Irix anymore)
For anything more involved than a few straightfoward lines, I'd probably still pick Perl 5. Very common, especially as some operating systems/distros have it in their core tooling (e.g. CentOS) and because it's included in git, so even available on Windows. Standard functionality is good enough and it's no big jump from sh/awk/sed. Rather do that before I depend on some obscure gawk function or gsed switch, especially as it's really hard to tell whether that's proprietary or in what version it was first introduced. Cross-browser checking is easier these days than cross-distro/unix.
Python does have a better/bigger standard library, but isn't as common and you might even run into Python 2/3 shenanigans these days.
Still, the situations where you have something moderately complex and can't install stuff should be pretty rare. Might not be able to do it for the whole system, but things like perlbrew/rbenv/nvm/pyenv-du-jour solve that mostly. At that level, Go might be an option, too.