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NameError: name 'sv' is not defined while importing python module

I am facing a problem in python. Tho the error is quite common, but since i am bit new to python, unable to comprehend the source hence asking you all. There are 2 modules: session.py and objects.py.
session.py
import copy
import pymongo
import spacy
import tweepy
import objects
objects.py:
import re
def refresh (sv = sv, obj = ''):
return 0
now, in python shell, i am getting the error before even executing objects.py:
$ python
Python 2.7.13 (default, Sep 26 2018, 18:42:22)
[GCC 6.3.0 20170516] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import session
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "session.py", line 6, in <module>
import objects
File "objects.py", line 3, in <module>
def refresh (sv = sv, obj = ''):
NameError: name 'sv' is not defined
>>>
I came from perl background to maybe missing some very common thing, but still i am able to do this:
>>> def ff(t): print t
...
In above, whitout defining t, it is working while in objects.py, how can i define sv without starting execution?

Why do I get a "symbol not found" for a found symbol in Pykd?

I'm working on a dump, which I try to investigate, using PYKD technology.
The result of the x /2 *!*``vtable' (just one backtick) contains the following result:
745293b8 mfc110u!CPtrList::`vftable'
However, when I try to get more information about this class, I get a "symbol not found" exception:
Python source code:
dprintln("name=[%s]" % type_stats.name)
if not type_stats.name in typesize_by_type:
try:
type_info = typeInfo(type_stats.name)
except Exception, e:
dprintln("text=[%s]" % (str(e)))
Output:
name=[mfc110u!CPtrList]
text=['CPtrList' - symbol not found]
The result of the lm command returns the mfc110u symbols, as you can see here:
0:000> lm
start end module name
...
744f0000 74930000 mfc110u (pdb symbols) C:\ProgramData\dbg\sym\mfc110u.i386.pdb\...\mfc110u.i386.pdb
...
For your information, I'm now working with the last version of PYKD:
0:000> .chain
Extension DLL search Path:
...
Extension DLL chain:
pykd.pyd: image 0.3.3.4, API 1.0.0, built Mon May 14 11:14:43 2018
[path: C:\Program Files (x86)\Windows Kits\10\Debuggers\x86\winext\pykd.pyd]
Meanwhile I've found a very simple way for reproducing the issue without needing to launch the whole script (using the Windbg prompt):
0:000> !py
Python 2.7.10 (default, May 23 2015, 09:40:32) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> typeInfo("mfc110u!CPtrList")
Traceback (most recent call last):
File "<console>", line 1, in <module>
SymbolException: 'CPtrList' - symbol not found
In addition to ussrhero's answer, there is following extra information:
The result of x /2 *!CPtrList* contains (amongst many others) the following results:
009530c4 <application>!CPtrList::~CPtrList
009530be <application>!CPtrList::CPtrList
... <application>!CPtrList::...
009abc5c <application>!CPtrList::`RTTI Base Class Array'
009abc4c <application>!CPtrList::`RTTI Class Hierarchy Descriptor'
009bcd18 <application>!CPtrList `RTTI Type Descriptor'
009abc30 <application>!CPtrList::`RTTI Base Class Descriptor at (0,-1,0,64)'
7464e9cb mfc110u!CPtrList::~CPtrList
74544a04 mfc110u!CPtrList::CPtrList
... mfc110u!CPtrList::...
745293b8 mfc110u!CPtrList::`vftable'
747510da mfc110u!CPtrList::`vector deleting destructor'
745293cc mfc110u!CPtrList::`RTTI Complete Object Locator'
7452940c mfc110u!CPtrList::`RTTI Base Class Array'
745293fc mfc110u!CPtrList::`RTTI Class Hierarchy Descriptor'
74795778 mfc110u!CPtrList `RTTI Type Descriptor'
745293e0 mfc110u!CPtrList::`RTTI Base Class Descriptor at (0,-1,0,64)'
746fdc68 mfc110u!CPtrList::classCPtrList
The script I'm using (heap_stat.py) browses through the results of !heap -h 0 and searches for the entry, corresponding with mfc110u!CPtrList::``vtable'.
The result of dt CPtrList starts with the following:
0:000> dt CPtrList
<application>!CPtrList => in other words, no 'mfcu110' entry
+0x000 __VFN_table : Ptr32
I'm already wondering for a long time, what's the difference between the mfc110u!CPtrList and the <application>!CPtrList entries and what's the exact role of the vtable entry in x /2 result?
Any ideas?
Thanks

Meanwhile I've found the solution:
Apparently for some objects, the module prefix needs to be removed:
>>> typeInfo("mdf110u!CPtrList")
-> SymbolException
>>> typeInfo("CPtrList")
-> this is working!!!

Try to see how WinDBG locates this type:
dt CPtrList
It maybe mfc110u does not contain type information fot CPtrList

Python os.environ throws key error?

I'm accessing an environment variable in a script with os.environ.get and it's throwing a KeyError. It doesn't throw the error from the Python prompt. This is running on OS X 10.11.6, and is Python 2.7.10.
What is going on?
$ python score.py
Traceback (most recent call last):
File "score.py", line 4, in <module>
setup_logging()
File "/score/log.py", line 29, in setup_logging
config = get_config()
File "/score/log.py", line 11, in get_config
environment = os.environ.get('NODE_ENV')
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/UserDict.py", line 23, in __getitem__
raise KeyError(key)
KeyError: 'NODE_ENV'
$ python -c "import os; os.environ.get('NODE_ENV')"
$
As requested, here's the source code for score.py
from __future__ import print_function
from log import get_logger, setup_logging
setup_logging()
log = get_logger('score')
And here's log.py
import json
import os
import sys
from iron_worker import IronWorker
from logbook import Logger, Processor, NestedSetup, StderrHandler, SyslogHandler
IRON_IO_TASK_ID = IronWorker.task_id()
def get_config():
environment = os.environ.get('NODE_ENV')
if environment == 'production':
filename = '../config/config-production.json'
elif environment == 'integration':
filename = '../config/config-integration.json'
else:
filename = '../config/config-dev.json'
with open(filename) as f:
return json.load(f)
def setup_logging():
# This defines a remote Syslog handler
# This will include the TASK ID, if defined
app_name = 'scoreworker'
if IRON_IO_TASK_ID:
app_name += '-' + IRON_IO_TASK_ID
config = get_config()
default_log_handler = NestedSetup([
StderrHandler(),
SyslogHandler(
app_name,
address = (config['host'], config['port']),
level = 'ERROR',
bubble = True
)
])
default_log_handler.push_application()
def get_logger(name):
return Logger(name)

Try running:
find . -name \*.pyc -delete
To delete your .pyc files.
Researching your problem I came across this question, where a user was experiencing the same thing: .get() seemingly raising a KeyError. In that case, it was caused, according to this accepted answer, by a .pyc file which contained code where a dict value was being accessed by key (i.e., mydict['potentially_nonexistent_key']), while the traceback was showing the code from the updated .py file where .get() was used. I have never heard of this happening, where the traceback references current code from a .py file, but shows an error raised by an outdated .pyc file, but it seems to have happened at least once in the history of Python...
It is a long shot, but worth a try I thought.

I encountered a similar error when I set the environment variable without exporting it. So if you do this:
me#host:/# NODE_ENV=foo
You will get this:
me#host:/# python3
Python 3.8.2 (default, Apr 27 2020, 15:53:34)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> node_env = os.environ['NODE_ENV']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.8/os.py", line 675, in __getitem__
raise KeyError(key) from None
KeyError: 'NODE_ENV'
>>>
But if you do this:
me#host:/# NODE_ENV=foo
me#host:/# export NODE_ENV
It works:
me#host:/# python3
Python 3.8.2 (default, Apr 27 2020, 15:53:34)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> node_env = os.environ['NODE_ENV']
>>> print(node_env)
foo
>>>

Command for windows to delete the .pyc files:
del /S *.pyc

I had the same problem. I solved that by making some corrections on the .env file:
Before:
Key = Value
After my correction:
Key=Value
without blank spaces and worked!

I was getting this error while trying to source from a .env file.
I didn't explicitly export the env vars so I had to change this.
ENVIRONMENT=DEV
to this
export ENVIRONMENT=DEV

Use export a=10 instead of a=10 while setting env variable. Add the same in ~./bashrc to reload the env var wherever you login.
Doing this resolved the issue

I'd recommend you start debugging os.py, for instance, on windows it's being used this implementation:
def get(self, key, failobj=None):
print self.data.__class__
print key
return self.data.get(key.upper(), failobj)
And if I test it with this:
import os
try:
os.environ.get('NODE_ENV')
except Exception as e:
print("-->{0}".format(e.__class__))
os.environ['NODE_ENV'] = "foobar"
try:
os.environ.get('NODE_ENV')
except Exception as e:
print("{0}".format(e.__class__))
The output will be:
<type 'dict'>
PYTHONUSERBASE
<type 'dict'>
APPDATA
<type 'dict'>
NODE_ENV
<type 'dict'>
NODE_ENV
So it makes sense the exception is not spawned reading dict.get docs.
In any case, if you don't want to mess up or debugging the python modules, try cleaning up the *.pyc files, try to set up properly NODE_ENV. And if all that don't work, restart your terminal to clear up.

How to workaround Python "WindowsError messages are not properly encoded" problem?

It's a trouble when Python raised a WindowsError, the encoding of message of the exception is always os-native-encoded. For example:
import os
os.remove('does_not_exist.file')
Well, here we get an exception:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
WindowsError: [Error 2] 系統找不到指定的檔案。: 'does_not_exist.file'
As the language of my Windows7 is Traditional Chinese, the default error message I get is in big5 encoding (as know as CP950).
>>> try:
... os.remove('abc.file')
... except WindowsError, value:
... print value.args
...
(2, '\xa8t\xb2\xce\xa7\xe4\xa4\xa3\xa8\xec\xab\xfc\xa9w\xaa\xba\xc0\xc9\xae\xd7\xa1C')
>>>
As you see here, error message is not Unicode, then I will get another encoding exception when I try to print it out. Here is the issue, it can be found in Python issue list:
http://bugs.python.org/issue1754
The question is, how to workaround this? How to get the native encoding of WindowsError?
The version of Python I use is 2.6.
Thanks.

We have the same problem in Russian version of MS Windows: the code page of the default locale is cp1251, but the default code page of the Windows console is cp866:
>>> import sys
>>> print sys.stdout.encoding
cp866
>>> import locale
>>> print locale.getdefaultlocale()
('ru_RU', 'cp1251')
The solution should be to decode the Windows message with default locale encoding:
>>> try:
... os.remove('abc.file')
... except WindowsError, err:
... print err.args[1].decode(locale.getdefaultlocale()[1])
...
The bad news is that you still can't use exc_info=True in logging.error().

sys.getfilesystemencoding() should help.
import os, sys
try:
os.delete('nosuchfile.txt')
except WindowsError, ex:
enc = sys.getfilesystemencoding()
print (u"%s: %s" % (ex.strerror, ex.filename.decode(enc))).encode(enc)
For other purposes than printing to console you may want to change final encoding to 'utf-8'

That is just the repr() string of the same error message. Since your console already supports cp950, just print the component you want. This works on my system after reconfiguring to use cp950 in my console. I had to explicitly raise the error message since my system is English and not Chinese:
>>> try:
... raise WindowsError(2,'系統找不到指定的檔案。')
... except WindowsError, value:
... print value.args
...
(2, '\xa8t\xb2\xce\xa7\xe4\xa4\xa3\xa8\xec\xab\xfc\xa9w\xaa\xba\xc0\xc9\xae\xd7\xa1C')
>>> try:
... raise WindowsError(2,'系統找不到指定的檔案。')
... except WindowsError, value:
... print value.args[1]
...
系統找不到指定的檔案。
Alternatively, use Python 3.X. It prints repr() using the console encoding. Here's an example:
Python 2.6.5 (r265:79096, Mar 19 2010, 21:48:26) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> '系統找不到指定的檔案。'
'\xa8t\xb2\xce\xa7\xe4\xa4\xa3\xa8\xec\xab\xfc\xa9w\xaa\xba\xc0\xc9\xae\xd7\xa1C'
Python 3.1.2 (r312:79149, Mar 21 2010, 00:41:52) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> '系統找不到指定的檔案。'
'系統找不到指定的檔案。'

Why would traceback.extract_stack() return [] when there is definitely a call stack?

I have a class that calls
traceback.extract_stack()
in its __init__(), but whenever I do that, the value of traceback.extract_stack() is [].
What are some reasons that this could be the case?
Is there another way to get a traceback that will be more reliable?
I think the problem is that the code is running in Pylons. Here is some code for a controller action:
def test_tb(self):
import traceback
return a.lib.htmlencode(traceback.extract_stack())
It generates a webpage that is just
[]
So, I don't think it has anything to do with being in the constructor of an object or anything like that. Could it have to do with an incompatibility between some kinds of threading and the traceback module or something like that?

Following shows traceback.extract_stack() working when called from a class's __init__ method. Please post your code showing that it doesn't work. Include the Python version. Don't type from memory; use copy/paste as I have done.
Python 2.6.2 (r262:71605, Apr 14 2009, 22:40:02) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import traceback as tb
>>> tb.extract_stack()
[('<stdin>', 1, '<module>', None)]
>>> def func():
... print tb.extract_stack()
...
>>> func()
[('<stdin>', 1, '<module>', None), ('<stdin>', 2, 'func', None)]
>>> class Klass(object):
... def __init__(self):
... print tb.extract_stack()
...
>>> k = Klass()
[('<stdin>', 1, '<module>', None), ('<stdin>', 3, '__init__', None)]
>>>
UPDATE Instead of looking at return a.lib.htmlencode(traceback.extract_stack()) and wondering, tap into the pipeline:
(1) do tb_stack = repr((traceback.extract_stack()) and write the result to your logfile for checking
(2) do return a.lib.htmlencode(some_known_constant_data) and check that the known data shows up correctly where you expect it to show up.

Looking at the code for the traceback module, one possibility is that you've got sys.tracebacklimit set to zero, though that seems like a longshot...

The reason turned out to be that someone turned on Pysco on the project, and Psyco doesn't play nice with the traceback module.