From xiaogang at gridmo.com  Thu Jul 14 11:08:32 2005
From: xiaogang at gridmo.com (John Xiaogang Zhang)
Date: Thu, 14 Jul 2005 19:08:32 +1000
Subject: [summerofcode] Problem in import
Message-ID: <42D62B90.4090300@gridmo.com>

Hi all,

I am a newbe in Python, and sometimes have problem with import.

Now I have a line

    from tilefilesys.tilefile import TFHandlers

in the top level module test.py. I have also tried to use

    import tilefilesys.tilefile.TFHandlers as TFHandlers

but the behaviour seems exactly the same.

The code in test.py calls other modules, some of them also use the 
similar import statement, and I got the following error message:

Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "test.py", line 29, in test
    from tilefilesys.tilefile import TFHandlers
  File "/home/xzhang/dev/TS/tilefilesys/tilefile/TFHandlers.py", line 
28, in ?
    from tilefilesys.tilefile.FmtVersn import *
  File "/home/xzhang/dev/TS/tilefilesys/tilefile/FmtVersn.py", line 163, 
in ?
    defaultVersnModule = loadTFModule( defaultVersionStr )
  File "/home/xzhang/dev/TS/tilefilesys/tilefile/FmtVersn.py", line 156, 
in loadTFModule
    return dynImport(__baseTFPackage + __availableVersions[versnStr])
  File "/home/xzhang/dev/TS/tilefilesys/common.py", line 401, in dynImport
    mod = __import__(modName, globals(), locals(), [])
  File "/home/xzhang/dev/TS/tilefilesys/tilefile/v1/__init__.py", line 
26, in ?
    import TFs
  File "/home/xzhang/dev/TS/tilefilesys/tilefile/v1/TFs.py", line 27, in ?
    from Fields import *
  File "/home/xzhang/dev/TS/tilefilesys/tilefile/v1/Fields.py", line 33, 
in ?
    from tilefilesys.tilefile import TFHandlers
ImportError: cannot import name TFHandlers


If I change the line in the last file (Fields.py) to

    import tilefilesys.tilefile.TFHandlers as TFHandlers

then the error becomes

  File "/home/xzhang/dev/TS/tilefilesys/tilefile/v1/Fields.py", line 32, 
in ?
    import tilefilesys.tilefile.TFHandlers as TFHandlers
AttributeError: 'module' object has no attribute 'TFHandlers'

However, if I change the last file to

    import tilefilesys.tilefile.TFHandlers as TFHandlers

that is, without the "as TFHandlers", then the errors gone (but I cannot 
refer it as the shorter reference).

Could please anyone tell me why it happens, and how to get rid off it?

Thank you in advance.

Xiaogang

From ianb at colorstudy.com  Thu Jul 14 17:25:56 2005
From: ianb at colorstudy.com (Ian Bicking)
Date: Thu, 14 Jul 2005 10:25:56 -0500
Subject: [summerofcode] Problem in import
In-Reply-To: <42D62B90.4090300@gridmo.com>
References: <42D62B90.4090300@gridmo.com>
Message-ID: <42D68404.8090609@colorstudy.com>

John Xiaogang Zhang wrote:
>     import tilefilesys.tilefile.TFHandlers as TFHandlers
> AttributeError: 'module' object has no attribute 'TFHandlers'
> 
> However, if I change the last file to
> 
>     import tilefilesys.tilefile.TFHandlers as TFHandlers
> 
> that is, without the "as TFHandlers", then the errors gone (but I cannot 
> refer it as the shorter reference).
> 
> Could please anyone tell me why it happens, and how to get rid off it?

Looks like a circular import; probably you import tilefile from 
somewhere, and tilefile imports this file, and this file then tries to 
import tilefile.  During that third import (the one with the error) the 
tilefile module has not been fully loaded, so the TFHandlers object has 
not yet been created.

You'll have to refactor your modules to avoid circular imports.

-- 
Ian Bicking  /  ianb at colorstudy.com  /  http://blog.ianbicking.org