Perl to Python Function translation [closed]

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I am trying to translate a Perl function into a Python function, but I am having trouble figuring out what some of the Perl to Python function equivalents.

Perl function:

sub reverse_hex {

 my $HEXDATE = shift;
 my @bytearry=();
 my $byte_cnt = 0;
 my $max_byte_cnt = 8;
 my $byte_offset = 0;
 while($byte_cnt < $max_byte_cnt) {
   my $tmp_str = substr($HEXDATE,$byte_offset,2);
    push(@bytearry,$tmp_str);
   $byte_cnt++;
   $byte_offset+=2;
 }
   return join('',reverse(@bytearry));
}

I am not sure what "push", "shift", and "substr" are doing here that would be the same in Python.

Any help will be much appreciated.

Answer 1

The Perl subroutine seems rather complicated for what it does, viz., taking chunks of two chars at a time (the first 16 chars) from the sent string and then reverses it. Another Perl option is:

sub reverse_hex {
    return join '', reverse unpack 'A2' x 8, $_[0];
}

First, unpack here takes two characters at a time (eight times) and produces a list. That list is reversed and joined to produce the final string.

Here's a Python subroutine to accomplish this:

def reverse_hex(HEXDATE):
    hexVals = [HEXDATE[i:i + 2] for i in xrange(0, 16, 2)]
    reversedHexVals = hexVals[::-1]
    return ''.join(reversedHexVals)

The list comprehension produces eight elements of two characters each. [::-1] reverses the list's elements and the result is joined and returned.

Hope this helps!

Answer 2

I realize that you are asking about the perl to python translation, but if you have any control over the perl, I would like to point out that this function is a lot more complicated than it needs to be.

The entire thing could be replaced with:

sub reverse_hex
{
  my $hexdate = shift;
  my @bytes = $hexdate =~ /../g;  # break $hexdate into array of character pairs
  return join '', reverse(@bytes);
}

Not only is this shorter, it is much easier to get your head around. Of course, if you have no control over the perl, you are stuck with what you were dealt.