Re: python. was COMMON rates (was RE: Congrads John Earl!)

[Hans Boldt <boldt@xxxxxxxxxx>]

Steve Richter wrote:
> Hans can I ask you to explain this python code a little bit?
>
> --------------------------------------------
> # Set up the replacement variables
> title = 'This is the title'
> body = '<p>This is the body</p>'
>
> # Write out the web page
> print template % vars()
> --------------------------------------------
>
> What is "vars()"?  a collection of all the variables in the current
> procedure?

Yes. More precisely, vars() is a built-in function that returns a 
dictionary of all the variables in the current scope.

A better way to code this would be to code a dictionary specifically 
for the replacement values to ensure separation between local 
variables and substitutions, but I thought using vars() would be 
easier to understand. That is, the better way to code it would be:

--------------------------------------------
# Set up the replacement variables
vars = {}
vars['title'] = 'This is the title'
vars['body'] = '<p>This is the body</p>'

# Write out the web page
print template % vars
--------------------------------------------

> What is "%"?  An argument seperator?

No, it is a string substitution operator. The first operand is a 
string containing % expressions which are substituted by elements of 
the  right-hand operand. For example, "..%s.."%"abc" yields the 
string "..abc..".

The right-hand operand may be a list, in which case the 
substitutions go by position (much like sprintf() in C). For 
example, "%s%d" %('a',17) gives you "a17".

If a dictionary is coded as right-hand operand, the substitution 
variables in the left-hand string can be identified by name. For 
example, "%(m)s%(n)d" % {'m':'a', 'n':17} gives you "a17".

> Is the "print" function able to retrieve the names of the variables and the
> values also?

I'm not sure I understand the question. The above code takes 
advantage of the % operator, which is not specific to the print 
statement. The print statement simply takes a list of values.

> If this is in the ballpark, can a programmer write a similar function that
> receives a collection of variables as a parm?

I'm not quite sure what you're asking here too, and I suspect my 
answer will miss the point of your question. Python has two built-in 
collection classes (to simplify a little bit): lists and 
dictionaries. These, like any other objects in the language, can be 
passed freely to functions.

> Does anything prevent python from running on the iSeries?

Ask Per Gummedal. Or try out his iSeries port at 
<http://home.no.net/pgummeda/>. I haven't tried it myself, so I 
can't comment personally on its quality. But the description at the 
web site seems reasonably up to date.

> Thanks.  Python looks like it is fun, but using procs, the current RPG could
> come close to your example like so:
>   template = ReadSourceMemberIntoString( Srcf: SrcMbr ) ;
>   AddToVarCollection( vars: 'Title': Title ) ;
>   AddToVarCollection( vars: 'Body': Body ) ;
>   ApplyVarsToTemplate( result, template, vars ) ;
>   WriteToStdOut( result ) ;

Python is indeed a lot of fun!

> And of course if RPG was open sourced, with IBM not losing any revenue
> because it stays a part of websphere, then RPG could be extended in
> experimental ways.  And the marketplace would decide if the extension is
> worthwhile or not.
>
> Steve Richter

I understand the rationale. But we'd probably need more people here 
to coordinate and validate the open-source changes to assure a 
reasonable level of quality.

Cheers! Hans