Instantiating classes on the fly

[vishalsethia]

Is there a way in which classes can be instantiated on the fly. I would be passed the name of the file to be instantiated through command line which I store in a variable using getopt.

So the file that needs to be instantiated would be dynamic. How would I achieve that in Python

Thanks
--V

[bartonc]

Is there a way in which classes can be instantiated on the fly. I would be passed the name of the file to be instantiated through command line which I store in a variable using getopt.

So the file that needs to be instantiated would be dynamic. How would I achieve that in Python

Thanks
--V

Hmmm... Maybe you mean instantiate objects on the fly... Anyway, that's what normally happens (on both cases)... To create a file object in your script from a command-line argument, use something like this:

import sys
# open a file in text mode for reading (create file object)
try:
    fileObj = open(sys.argv[1])
    # print each line as an example of doing something with a file object
    for line in fileObj:
        print line
    fileObj.close()
except (IOError, IndexError):
    print "No such file"

[vishalsethia]

Sorry for not being clear on the first post. What I meant was

Script 1
---------------
./script1.py -f script2.py

To instantiate script2 , one would normally use in script1

object = script2.script2()
object.function1()

But if the name of script2 is dynamic (which comes from command line), how do I instantiate that object.


Script 2 (script2.py)
------------

class script2:
       def __init__(self):
              .........
              print "In script 2 "
       def function1(self):
              print "Function1 "
 

Thanks

[bartonc]

Sorry for not being clear on the first post. What I meant was

Script 1
---------------
./script1.py -f script2.py

To instantiate script2 , one would normally use in script1

object = script2.script2()
object.function1()

But if the name of script2 is dynamic (which comes from command line), how do I instantiate that object.


Script 2 (script2.py)
------------

class script2:
       def __init__(self):
              .........
              print "In script 2 "
       def function1(self):
              print "Function1 "
 

Thanks

__import__(filename) # leave off the .py

[vishalsethia]

Thanks Barton, That helped me import the module but now how do I instantiate it or access the functions declared within that class.

Thanks
--V

[Motoma]

Barton! This sounds like a perfect oportunity for abstract classes! I've never done anything with python and inheritance, however, so I would appreciate your input.

[vishalsethia]

Was googling around and found a way to instantiate objects on the fly.

Script 1 (Arbitrary.py)
--------------

import string
class ArbitraryClass:
        def getClass(self, moduleName):
                return __import__(
                        moduleName,
                        {},
                        {},
                        []
                        )
 

In your script which would instantiate other objects
Script2
------------

arb = Arbitrary.ArbitraryClass()
instance = getattr( arb.getClass("FILENAME"), "CLASSNAME")()
instance.any_function in that class 
 

where FILENAME is without .py extension and CLASSNAME is the name of the class that is defined within that FILE.

Thanks

[Motoma]

Glad to see you've gotten it sorted out. Thanks for posting back the answer.