Passing a string argument by reference

[Andrew Chalk]

Thanks. You guessed correctly about what I am trying to do although I think
the syntax is:

self.txtCIF = self.form.getvalue('txtCIF', self.txtCIF)

Regards

"Irmen de Jong" <irmen at -NOSPAM-REMOVETHIS-xs4all.nl> wrote in message
news:3f2d728a$0$49117$e4fe514c at news.xs4all.nl...
> Andrew Chalk wrote:
> > I am a raw beginner to Python. I just read in "Learning Python" that
> > assigning to a string argument inside a function does not change the
string
> > in the caller. I want an assignment in the function to alter the passed
> > string in the caller. Is there any way to do this?
>
> No. Strings are immutable. However, there is a better solution to do what
> you want: just return the new value as a result of the function, and
> let the caller process this further.
>
> Example:
>
> def addBarToString(variable):
>      return variable+"bar"
>
> called with:
>
> variable="foo"
> variable=addBarToString(variable)
> print variable
>
> results in >>foobar<< to be printed.
>
>
> > For example
> >
> > def SafeAdd(self, Variable, Value):
> >     if self.form.has_key( Value ):
> >     Variable = self.form[Value].value
> >
> > Called with:
> >
> > self.SafeAdd(self.txtCIF, 'txtCIF')
> >
> > self.CIF is not changed on return from the function. How do I modify
this so
> > that it is?
>
> I understand that you want to assign self.txtCIF  (not self.CIF as you
> wrote) the value of self.form['txtCIF'], but only if that value
> occurs in self.form?
>
> There is a much easier way to do this. I suspect that self.form is
> a dictionary (or a dict-like object).
>
> Just use:
>
>    self.txtCIF = self.form.get('txtCIF', self.txtCIF)
>
> The second argument to the get method is the default value that is
> returned if the required key is not present in the dict.
> In this case, it returns the 'old' value of self.txtCIF, so in effect,
> self.txtCIF will be unchanged if 'txtCIF' does not occur in self.form.
> Also see http://www.python.org/doc/current/lib/typesmapping.html
>
> Hope this helps!
> --Irmen de Jong
>