[Tutor] Convert string to variable name

[Danny Yoo]

On Wed, 26 Jan 2005, Tony Giunta wrote:

> This is something I've been trying to figure out for some time.  Is
> there a way in Python to take a string [say something from a raw_input]
> and make that string a variable name?


Hi Tony,

Conceptually, yes: you can collect all those on-the-fly variables in a
dictionary.


> I'm sure I could accomplish something similar using a plain old
> dictionary,

Yup.  *grin*


> but I was playing around with the OOP stuff and thought it might be a
> neat thing to try out.

We can use exec() to create dynamic variable names, but it's almost always
a bad idea.  Dynamic variable names make it very difficult to isolate
where variables are coming from in a program.  It'll also prevent us from
reliably using the excellent PyChecker program:

    http://pychecker.sourceforge.net/

So I'd recommend just using a plain old dictionary: it's not exciting, but
it's probably the right thing to do.



Looking back at the code:

###
def generateInstance():
        class test:
                def __init__(self, title, price):
                        self.title = title
                        self.price = price
                def theTitle(self, title):
                        return self.title
                def thePrice(self, price):
                        return self.price

        myName = raw_input("Name: ")
        myTitle    = raw_input("Title: ")
        myPrice  = raw_input("Price: ")

        exec '%s = test("%s", %s)' % (myName, myTitle, myPrice)
###


In Python, we actually can avoid writing attribute getters and setters ---
the "JavaBean" interface --- because Python supports a nice feature called
"properties".  See:

    http://dirtsimple.org/2004/12/python-is-not-java.html
    http://www.python.org/2.2.2/descrintro.html#property



The upside is that we usually don't need methods like theTitle() or
thePrice() in Python.  Our revised code looks like:

###
class test:
    def __init__(self, title, price):
        self.title = title
        self.price = price

instances = {}

def generateInstance():
    myName  = raw_input("Name: ")
    myTitle = raw_input("Title: ")
    myPrice = raw_input("Price: ")
    instances[myName] = test(myTitle, myPrice)
###



If you have more questions, please feel free to ask.  Best of wishes to
you!