Inheritance

[Duncan Booth]

HMS Surprise <john at datavoiceint.com> wrote:

> I am trying to understand the 'if' statement and the exec statement in
> the code below. 
> 
> from PyHttpTestCase import PyHttpTestCase
> from com.bitmechanic.maxq import Config
> global validatorPkg
> if __name__ == 'main':
>     validatorPkg = Config.getValidatorPkgName()
> # Determine the validator for this testcase.
> exec 'from '+validatorPkg+' import Validator'

'global' inside a function makes a name have global scope in the function 
where it would otherwise have been local. 'global' at file scope is 
completely pointless.

> In particular what is the purpose of the
> surrounding plus signs?

The plus sign are simply concatenating strings.

exec should generally be avoided for several reasons. Here it is being used 
simply to import from a module whose name has been determined at runtime: a 
call to the __import__ builtin could be used for the same thing.

> May I assume the if statement overrides an
> imported assignment statement.

There isn't anything in the code you pasted which could be assigning to the 
name validatorPkg. If the code is run as the main script then validatorPkg 
is set to some value. If the code is imported as a module then validatorPkg 
will (unless there is some very convoluted code) be unset when the exec is 
executed.

It would appear that the 'if' statement serves purely to make the code fail 
if it is imported as a module.