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ImportError: cannot import name dns

Prasad, Ramit ramit.prasad at jpmorgan.com
Tue Sep 13 19:09:50 EDT 2011 
-----Original Message-----
From: python-list-bounces+ramit.prasad=jpmorgan.com at python.org [mailto:python-list-bounces+ramit.prasad=jpmorgan.com at python.org] On Behalf Of Jack Bates
Sent: Tuesday, September 13, 2011 5:28 PM
To: python-list at python.org
Subject: ImportError: cannot import name dns

Why is the following ImportError raised?

$ ./test
Traceback (most recent call last):
  File "./test", line 3, in <module>
    from foo import dns
  File "/home/jablko/foo/dns.py", line 1, in <module>
    from foo import udp
  File "/home/jablko/foo/udp.py", line 1, in <module>
    from foo import dns
ImportError: cannot import name dns
$

I reproduce this error with the following four files and five lines:

== foo/dns.py ==
from foo import udp

== foo/udp.py ==
from foo import dns

== foo/__init__.py ==
(empty)

== test ==
#!/usr/bin/env python

from foo import dns


===========================================================================
 
It is a circular dependency. Dns will try to import udp which will in turn import dns (again) in an endless cycle; instead an ImportError is raised. 

Circular dependency is a Bad Thing.

Ramit


Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423


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