Module imports during object instantiation

[Ritesh Raj Sarraf]

Bruno Desthuilliers wrote:

>>> What's leading you to conclude the import isn't being executed? You
>>> realise, I trust, that the module's code will only be executed on the
>>> first call to __init__()?
>>>
>> 
>> Well. Putting it in a "try" inside __init__() doesn't do anything.
> 
> This would be highly suprising.
>

Yes, it is surprising. Unfortunately. :-(
Or maybe I'm doing something really dumb.
 
>> The
>> import never happens.
> 
> As soon as your running this code on a platform where os.name yields
> either 'nt' or 'dos', the import statement is executed. You can bet your
> ass on this. Now this import can fail for a lot of reasons (imported
> module not in sys.path, error in the imported module, etc), and since
> your catching *and dismissing* the ImportError, you don't know what
> effectively happens. It's like someone send you mails, you set your
> filter to trash mails from this person, and then complain this person
> never send you mails !-)
> 
>> And thus if I make a call in any of the methods, it
>> fails with an error message. A NameError IIRC.
> 
> "IIRC" ? Inspecting the traceback may help, you know.

There's no traceback because the import never happens.

Here's what I've captured for you exactly I see on my terminal


rrs at learner:/tmp$ cat rick.py
class Log:
    def __init__(self, verbose, lock = None):
        self.VERBOSE = bool(verbose)
        self.lock = bool(lock)

        if self.lock:
            self.dispLock = threading.Lock()
        else:
            self.dispLock = None

        if os.name == 'posix':
            try:
                import foobar
            except ImportError, e:
                print >> sys.stderr, e

            self.platform = 'posix'
            self.color = get_colors()

        elif os.name in ['nt', 'dos']:
            self.platform = 'microsoft'
            try:
                import SomeModule
            except ImportError, e:
                # comment out next line before going to prod...
                print >> sys.stderr, e

                self.color = None
            else:
                self.color = SomeModule.get_colors_windows()
        else:
            self.platform = None
            self.color = None
rrs at learner:/tmp$ python
Python 2.4.4 (#2, Jul 21 2007, 11:00:24)
[GCC 4.1.3 20070718 (prerelease) (Debian 4.1.2-14)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os, sys
>>> os.path.abspath(os.curdir)
'/tmp'
>>> from rick import Log
>>> import rick
>>> os.name
'posix'
>>> import foobar
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ImportError: No module named foobar
>>>



For the 'posix' OS, I'm doing an erratic import which should fail and print
the error message.

See, it prints nothing. This _is_ what has made me conclude that imports
aren't executed in __init__(). But hey, they will get executed if you put
them in any of the methods (which is again illogical because methods
can/are called multiple times).

Ritesh
-- 
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