printing a variable in python

Question

I have this python code which set A or B in a class. I want to print what this class receives:

if options.A:
   print "setting A"
   class TmpClass(A): pass
else:
   print "nothing set in the command line => setting to B"
   class TmpClass(B): pass

print "selected=",TmpClass

I want to see either A or B in the output but I see:

selected= TmpClass

This looks really weird. Are you quite sure you know what you are doing? If not, please research OOP again, because apparently you did not understand the concept. — Till Helge
– Till Helge, Commented Nov 22, 2011 at 9:16
Do you have two classes A and B? Because what you are doing is creating a new class TmpClass that inherits from either A or B. — Some programmer dude
– Some programmer dude, Commented Nov 22, 2011 at 9:25
Sorry.... That question does not represent my problem. I will try to edit it soon. — mahmood
– mahmood, Commented Nov 22, 2011 at 9:27

mac · Accepted Answer · 2011-11-22 09:42:51Z

3

What your code is doing, translated in English is:

if option.A has a value that evaluates to True:
    define an empty class called "TmpClass" that inherits from the object called "A"
otherwise:
    define an empty class called "TmpClass" that inherits from the object called "B"

Now, if what the code is actually doing is indeed what you intended, my guess is that what you wanted could be to know whether your class is A or B -based... If I am right, then the line you want to have at the end is:

print('TmpClass inherits from : %s' % TmpClass.__bases__)

HTH!

edited Nov 22, 2011 at 9:42

answered Nov 22, 2011 at 9:34

mac

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1 Comment

mahmood Over a year ago

brilliant... that was exactly what I meant :)

Some programmer dude · Accepted Answer · 2011-11-22 09:23:47Z

1

You can assign classes to a variable, without creating instances of them:

if options.A:
   print "setting A"
   TmpClass = A
else:
   print "nothing set in the command line => setting to B"
   TmpClass = B

print "selected=",TmpClass

answered Nov 22, 2011 at 9:23

Some programmer dude

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Comments

Adam Morris · Accepted Answer · 2011-11-22 09:38:44Z

You might look at using isinstance(). For example:

class MyBaseClass():
    def __init__(self):
        self.cType = 'Base'

    def whichClass(self):
        print 'Class type = {0}'.format(self.cType)

        if isinstance(self,DerivedClassA):
            print 'Derived Class A'
        elif isinstance(self,DerivedClassB):
            print 'Derived Class B'
        elif isinstance(self,MyBaseClass):
            print 'Not A or B'
        else:
            print 'Unknown Class'

class DerivedClassA(MyBaseClass):
    def __init__(self):
        self.cType = 'Class A'

class DerivedClassB(MyBaseClass):
    def __init__(self):
        self.cType = 'Class B'


Then Run:

base = MyBaseClass()
a = DerivedClassA()
b = DerivedClassB()
a.whichClass()
>> Class type = Class A
>> Derived Class A
b.whichClass()
>> Class type = Class B
>> Derived Class B
base.whichClass()
>> Class type = Base
>> Not A or B

Dogbert · Accepted Answer · 2011-11-22 09:17:40Z

0

A and B are formal arguments passed to the class here, not actual values of A and B.

answered Nov 22, 2011 at 9:17

Dogbert

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