[Tutor] Help Passing Variables

Dave Angel d at davea.name
Fri Oct 19 23:42:10 CEST 2012

On 10/19/2012 11:40 AM, Daniel Gulko wrote:
> Thanks David. This has been helpful in understanding a bit more on how parameters are passed through.

Please don't top-post.  it ruins the sequence of events. Your comments
above happened after the parts you quote below.  So why are they not
after the things they follow?  There is a long-standing convention in
this forum, and many others, and why let Microsoft ruin it for all of us?

>> Date: Thu, 18 Oct 2012 04:44:55 -0400
>> Subject: Re: [Tutor] Help Passing Variables
>> From: dwightdhutto at gmail.com
>> To: dangulko at hotmail.com
>> CC: tutor at python.org
>> #A little more complex in terms of params:
>> def SwapCaseAndCenter(*kwargs):

By convention kwargs is used for keyword arguments, while the * means
positional arguments.  The function uses none of them, so it's all
bogus.  You can't learn anything useful about argument passing from this
example code, except what NOT to do.

>> 	if upper_or_lower == "upper":
>> 		print a_string.center(center_num).upper()
>> 	if upper_or_lower == "lower":
>> 		print a_string.center(center_num).lower()

To understand the most elementary aspects of function passing, let's
write a whole new function, and call it a few times.  Paste this into a
file, and try various things, and make sure you see how they work.  Or
reread Alan's email, which was also correct and clear.

First point, a simple function may take zero arguments, or one, or two,
or fifty.  We'll start with positional arguments, which means order
matters.  Python also supports keyword arguments, default values, and
methods, none of which I'll cover here.

When you define a function, you specify its formal parameters.  You do
that by putting the parameter names inside the parentheses.  Unlike most
languages, you do NOT specify the types of any of these.  But the order
matters, and the number matters.

So if we define a function:

def truncate_string(a_string, width):
    temp = a_string[:width]
    return temp

That function needs to be called with two arguments, which match the two formal parameters.  They do NOT have to have the same names, and in fact they might well be literal strings or ints, or variables with string and int values.

print truncate_string("this is a long string", 4)

should print out "this"  (without the quotes, of course)

name = raw_input("give me a name")
trunc_name = truncate_string(name, 8)
print trunc_name

truncate_string("aaa")     #gives error, because it has the wrong number of arguments

Does this help?



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