AttributeError: 'module' object has no attribute '_trace_level'

[misery]

Issue description:
After an upgrade from 3.0.0 to 3.1.0 I cannot login into my review board as the ldap module throws an error. After an downgrade everything works fine.

Steps to reproduce:

[...]
  File "/opt/reviewboard/dist/lib/python2.7/site-packages/reviewboard/accounts/backends.py", line 1008, in authenticate
    for uri, connection in self.get_ldap_connections(userdomain):

  File "/opt/reviewboard/dist/lib/python2.7/site-packages/reviewboard/accounts/backends.py", line 935, in get_ldap_connections
    connection = ldap.initialize(ldap_uri)

  File "/opt/reviewboard/dist/lib/python2.7/site-packages/ldap/functions.py", line 85, in initialize
    return LDAPObject(uri,trace_level,trace_file,trace_stack_limit,bytes_mode)

  File "/opt/reviewboard/dist/lib/python2.7/site-packages/ldap/ldapobject.py", line 99, in __init__
    self._trace_level = trace_level or ldap._trace_level

AttributeError: 'module' object has no attribute '_trace_level'

Operating system: Linux
Python version: 2.7.14
python-ldap version: 3.1.0 and 3.0.0

[Xophmeister]

I am able to replicate this -- and came to post an issue -- but only when running Python with optimisations enabled (i.e., python -O or python -OO).

Steps to reproduce:

In test.py:

import ldap
ldap.initialize("ldap://my.ldap.host")

Then at the command line:

$ python -O test.py
Traceback (most recent call last):
  File "test.py", line 3, in <module>
    server = ldap.initialize("ldap://my.ldap.host")
  File "/Users/ch12/Projects/play/python/ldap/.venv/lib/python3.6/site-packages/ldap/functions.py", line 85, in initialize
    return LDAPObject(uri,trace_level,trace_file,trace_stack_limit,bytes_mode)
  File "/Users/ch12/Projects/play/python/ldap/.venv/lib/python3.6/site-packages/ldap/ldapobject.py", line 99, in __init__
    self._trace_level = trace_level or ldap._trace_level
AttributeError: module 'ldap' has no attribute '_trace_level'

This is with Python 3.6.5 on macOS 10.11.6, with python-ldap 3.1.0

[chiragsoni2401]

I am facing the same issue on windows machine with python v3.7.2 and python-ldap 3.1.0
I tried to downgrade to python-ldap to 2.5.2 but even not able to install it. Getting following error.

python_ldap-2.5.2-cp27-cp27m-win_amd64.whl is not a supported wheel on this plat
form.

[encukou]

Pull request #234 should fix the problem. I'd be grateful if you could check if the change fixes the issue.

[Battlesheepu]

I find it a bit scary that, once __debug __ is off (which should be in prod) and this very argument is not passed, the app simply fails when initializing a connection.

As a quick workaround I recommend passing pretty much anything as trace_level when initializing connection - as long as the value does not evaluate to False. '0' would be a good example - although this will crash under __debug __.

For prod:

connection = ldap.initialize(ldap_uri, trace_level='0')

For debug:

connection = ldap.initialize(ldap_uri)

[encukou]

Again: Pull request #234 should fix the problem.
I'd be grateful for a review, so the change can get out.