Using C or Python or Perl does not automatically keep people from failing to check whether some code that reaches out into the environment to prepare for later action actually succeeded.
It tends to fail much more noisily if you try to use an uninitialized variable - C will probably segfault (or end up removing a garbage string of probably-unprintable characters), Python and Perl will throw exceptions.
I don't see any way to accidentally write code in C or Python (Perl may be a different beast as a sibling comment indicates) that deletes the user's home directory if an environment variable is unset. These languages don't keep you from failing to check, but they fail much better. An unset environment variable without a check means you'll probably crash, whereas with a shell script you just keep on going, with bad data.