getattr() question

[Sledge]

Hi.

I am trying to dynamically load a class and attributes at run time. I
do not know what classes will be referenced until run time. I have it
loading the module correctly, but when I use getattr to access the
class and its attributes everything works except that I get additional
unwanted output. The code



testclass.py:

#!/usr/bin/python

class testclass(object):

myname = ""

def __init__(self, name):
self.myname = name

def view(self):
print "hello %s" % self.myname



test.py:

#!/usr/bin/python

import sys
sys.path.append('.')
from pprint import pprint

if __name__ == '__main__':
myname = "testclass"
myaction = "view"
try:
tc = __import__(myname)
myclass = getattr(tc,myname)
myinstance = getattr(myclass('python n00b'), myaction,
myaction)
pprint(myinstance())
except ImportError:
"error"



Here is the output that I get:

user@debian:~/$ python test.py
hello python n00b
None
user@debian:~/$


Why is it printing 'None'? What am I doing wrong. I appreciate any
help.

 

[John Machin]

Hi.

I am trying to dynamically load a class and attributes at run time. I
do not know what classes will be referenced until run time. I have it
loading the module correctly, but when I use getattr to access the
class and its attributes everything works except that I get additional
unwanted output. The code

testclass.py:

#!/usr/bin/python

class testclass(object):

myname = ""

def __init__(self, name):
self.myname = name

def view(self):
print "hello %s" % self.myname

test.py:

#!/usr/bin/python

import sys
sys.path.append('.')
from pprint import pprint

if __name__ == '__main__':
myname = "testclass"
myaction = "view"
try:
tc = __import__(myname)
myclass = getattr(tc,myname)
myinstance = getattr(myclass('python n00b'), myaction,
myaction)
pprint(myinstance())
except ImportError:
"error"

What do you expect to see if the import fails?

Here is the output that I get:

user@debian:~/$ python test.py
hello python n00b
None
user@debian:~/$

Why is it printing 'None'? What am I doing wrong. I appreciate any
help.

The problem is nothing to do with using getattr; it "works" in the
sense that it does what you appear to want it to.

You have *two* explict outputting statements: the print statement in
the first file and the pprint invocation in the second file. Seems
fairly obvious that it's not the first of these. So dissect
"pprint(myinstance())".

myinstance is bound to the view method [in the first file] which
(implicitly) returns None. So you are in effect doing pprint(None).

Aside: give your fingers a rest: don't type "my" so often.

 

[Sledge]

Hi.

I am trying to dynamically load a class and attributes at run time. I
do not know what classes will be referenced until run time. I have it
loading the module correctly, but when I use getattr to access the
class and its attributes everything works except that I get additional
unwanted output. The code


class testclass(object):

myname = ""

def __init__(self, name):
self.myname = name

def view(self):
print "hello %s" % self.myname


import sys
sys.path.append('.')
from pprint import pprint

if __name__ == '__main__':
myname = "testclass"
myaction = "view"
try:
tc = __import__(myname)
myclass = getattr(tc,myname)
myinstance = getattr(myclass('python n00b'), myaction,
myaction)
pprint(myinstance())
except ImportError:
"error"

What do you expect to see if the import fails?

Here is the output that I get:

user@debian:~/$ python test.py
hello python n00b
None
user@debian:~/$

Why is it printing 'None'? What am I doing wrong. I appreciate any
help.

The problem is nothing to do with using getattr; it "works" in the
sense that it does what you appear to want it to.

You have *two* explict outputting statements: the print statement in
the first file and the pprint invocation in the second file. Seems
fairly obvious that it's not the first of these. So dissect
"pprint(myinstance())".

myinstance is bound to the view method [in the first file] which
(implicitly) returns None. So you are in effect doing pprint(None).

that did the trick. How could I have missed something so obvious?

Aside: give your fingers a rest: don't type "my" so often.

It was just for demonstration purposes . Thanks for your help John.