TypeError: unbound method PrintInput() must be called with test instance as first argument (got test instance instead)

[Peter Otten]

arotem wrote:

> Hi,
> 
> I am trying to call an unbound method (PrintInput) with the object
> instance as the first argument but getting the following error:
> "TypeError: unbound method PrintInput() must be called with test
> instance as first argument (got test instance instead)"
> 
> Below is the sample code (test) for this purpose (two files).
> 
> Any help is greatly appreciated.
> 
> Thanks in Advance, Anat
> 
> 
> Sample Code:
> 
> File 1 - input_file.py:
> 
> #!/usr/bin/env python
> from test import *
> 
> CMD = (test.PrintInput, float(2))
> 
> File 2 - test.py:
> 
> from input_file import *
> 
> class test:
>     def __init__(self):
>         _test = 2
>     def PrintInput(self, input):
>         print "Input is = %s"%(input)
> 
> if __name__== "__main__":
>     print "Unit testing"
>     inst = test()
>     print CMD
>     cmd = CMD[0]
>     param = CMD[1:]
>     
>     cmd(inst,param)        # this is the problematic line

It is best to avoid situations where you import the main script into modules
used by your program. You end up with to copies of (in your example)
test.py. and therefore two functionally identical but distinct test classes
and that gets you the error message. You can verify that with the following
demo:

#file script_is_main.py
import script_is_main
import __main__

print script_is_main is __main__ # False

A sound layout would instead be to move the test class into a separate
module that is used by both the main script and the test module:

# file test.py
class Test:
    def __init__(self):
        _test = 2
    def PrintInput(self, input):
        print "Input is = %s"%(input)

# file input_file.py
import test

CMD = (test.Test.PrintInput, float(2))

# file main.py
#!/usr/bin/env python
import input_file
import test

if __name__== "__main__":
    print "Unit testing"
    inst = test.Test()
    CMD = input_file.CMD
    print CMD
    cmd = CMD[0]
    param = CMD[1:]

    cmd(inst, param) # this was the problematic line

Peter