Emulating Pascal input

[Jeff Shannon]

In article <acjjmf$rgf$0 at 216.39.172.122>, Bengt Richter says...

> If you pass a _string_ containing an ordered arg name list 
> (e.g., comma-separated as below), you can get the names bound
> in the global name space to converted values.

Just skimming, so I may have missed something, but ISTM that this 
method of doing things is very fragile.  You can use this to 
rebind *global* variables... but once you put those variables 
(and the input call) inside of another function, suddenly it 
breaks for no apparent reason.  This will be very surprising to 
students who probably won't understand all of the hidden 
complexities of global vs local namespaces.

As Bengt says, this is shoehorning ideas that don't fit well into 
Python.  I think that it is better for the students if they learn 
Python conventions instead of Pascal conventions poorly 
translated into Python.  (If you really want them to learn the 
Pascal conventions, then keep teaching them Pascal. <wink>)

My loose translation of the readin() function would be something 
like this:

def readin(prompt, numtype=int):
    data = raw_input(prompt)
    numbers = data.split()
    return map(numtype, numbers)

This will allow any number of whitespace-separated numbers to be 
entered, and will return all of them in a list.  It defaults to 
returning ints, but can be used to return floats or longs or 
complex by using the optional second argument.  I would argue 
that this teaches *better* programming practice than the Pascal 
version, since it doesn't depend on side-effects to the 
function's arguments.  <wink>

Some modification could be made to this to allow it to read from 
a file, too.  Personally, though, I'd be tempted to separate the 
(string) input retrieval from the processing.  This makes it a 
two-step operation, but it's clear what's going on.

def process_input(data, numtype=int):
    numbers = data.split()
    return map(numtype, numbers)

x, y = process_input(raw_input("Enter two numbers: "))
I, j, k = process_input(infile.readline())

(As a disclaimer, I'm not really familiar with Pascal, so please 
take all my comments regarding it in the lighthearted vein in 
which they are intended.)

-- 

Jeff Shannon
Technician/Programmer
Credit International