Question

I am new to perl, at most places where hash is used a reference to python’s dictionaries is given. A difference which I have noticed is that the hashes don’t preserve the order of elements. I would like to know if there are some more concrete and fundamental differences between the two.

Answer 1

The most fundamental difference is that perl hashes don’t throw errors if you access elements that aren’t there.

$ python -c 'd = {}; print("Truthy" if d["a"] else "Falsy")'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
KeyError: 'a'
$ perl -we 'use strict; my $d = {}; print $d->{"a"} ? "Truthy\n": "Falsy\n"'
Falsy
$ 

Perl hashes auto create elements too unlike python

$ python -c 'd = dict(); d["a"]["b"]["c"]=1'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
KeyError: 'a'
$ perl -we 'use strict; my $d = {};  $d->{a}{b}{c}=1'
$

If you are converting perl to python those are the main things that will catch you out.