[perl-python] 20050116 defining a function

[Xah Lee]

© # the following is a example of defining
© # a function in Python.
©
© def fib(n):
© """This prints n terms of a sequence
© where each term is the sum of previous two,
© starting with terms 1 and 1."""
© result=[];a=1;b=1
© for i in range(n):
© result.append(b)
© a,b=b,a+b;
© result.insert(0,1)
© del result[-1]
© return result
©
© print fib(6)
©
© # note the use of .insert to insert 1 at
© # the beginning of a list, and Òdel
© # result[-1]Ó to remove the last element
© # in a list. Also, the string
© # immediately following the function
© # definition is the function's
© # documentation.
©
© # the unusual syntax of a.insert() is
© # what's known as Object Oriented syntax style.
©
© # try writing a factorial function.
©
© -------------------
© # the equivalent perl version is this:
©
© =pod
©
© fib(n) prints n terms of a sequence where each
© term is the sum of previous two,
© starting with terms 1 and 1.
©
© =cut
©
© use strict;
© my @result;
© my ($a, $b);
©
© sub fib($) {
© my $n= @_[0];
© @result=();$a=1;$b=1;
© for my $i (1..$n){
© push @result, $b;
© ($a,$b)=($b,$a+$b);
© }
© unshift @result, 1;
© pop @result;
© return @result;
© }
©
© use Data:umper;
© print Dumper [fib(5)];
©
© # the =pod and =cut
© # is perl's way of demarking inline
© # documentation called POD.
© # see Òperldoc -t perlpodÓ
© # note: the empty line around it
© # is necessary, at least in perl version
© # 5.6 up to ~2002.
©
© # the Òuse strict;Ó is to make perl's
© # loose syntax stricter by enforcement.
© # Its use is encouraged by
© # perl gurus, but not all standard
© # packages use it.
©
© # the ÒmyÓ are used to declare variables.
© # necessary under Òuse strict;Ó
© # see Òperldoc -t strictÓ
©
© # the $ in fib($) is there to declare
© # that fib has a parameter of one scalar.
© # Its use is however optional and uncommon.
© # it is used for clarity but
© # has also met with controversy by
© # perl gurus as being unperl.
© # see Òperldoc perlsubÓ for ref.
©
© # the @_[0] is the first element of the
© # array @_. The @_ array is a predefined
© # array, holding arguments to subroutines.
© # see Òperldoc -t perlvarÒ
©
© # see
© # perldoc -tf unshift
© # perldoc -tf pop
©
© # the last line, [fib(5)], is basically
© # to make it a memory address of a copy of
© # the list returned by fib(5), so that
© # Dumper can print it.
© # see Òperldoc -t perldataÓ or perlref
© # for unix-styled technicalities.
©
© Xah
© (e-mail address removed)
© http://xahlee.org/PageTwo_dir/more.html

 

[Ala Qumsieh]

© my $n= @_[0];

Do you ever test your code before making fun of yourself in front of
millions?

*plonk*

--Ala

 

[Fredrik Lundh]

© my $n= @_[0];

Do you ever test your code before making fun of yourself in front of millions?

this perl usability study is getting more and more interesting. who
needs television?

</F>

 

[Xah Lee]

errata:

* the variables in the perl section should be declared inside the
subroutine.
* the @_[0] should've been $_[0]

thanks for Dave Cross for pointing them out.

* the Mathematica Apply should be Select...
Xah
(e-mail address removed)
http://xahlee.org/PageTwo_dir/more.html

 

[Chris Mattern]

errata:

* the variables in the perl section should be declared inside the
subroutine.
* the @_[0] should've been $_[0]

thanks for Dave Cross for pointing them out.

* the Mathematica Apply should be Select...
Xah
(e-mail address removed)
http://xahlee.org/PageTwo_dir/more.html

Here's a thought: don't post code you haven't tested!
--
Christopher Mattern

"Which one you figure tracked us?"
"The ugly one, sir."
"...Could you be more specific?"

 

[Tad McClellan]

Xah Lee wrote:

*plonk*

Man, you are way behind the curve.

I did that over 3 years ago! [1]




[1] Message-ID: <[email protected]>

I followed the link in that post on a hunch, and found
he says himself that he is a troll. Go figure...