I"m at wit"s end. After a dozen hours of troubleshooting, probably more, I thought I was finally in business, but then I got:
Model class django.contrib.contenttypes.models.ContentType doesn"t declare an explicit app_label
There is SO LITTLE info on this on the web, and no solution out there has resolved my issue. Any advice would be tremendously appreciated.
I"m using Python 3.4 and Django 1.10.
From my settings.py:
INSTALLED_APPS = [
"DeleteNote.apps.DeletenoteConfig",
"LibrarySync.apps.LibrarysyncConfig",
"django.contrib.admin",
"django.contrib.auth",
"django.contrib.contenttypes",
"django.contrib.sessions",
"django.contrib.messages",
"django.contrib.staticfiles",
]
And my apps.py files look like this:
from django.apps import AppConfig
class DeletenoteConfig(AppConfig):
name = "DeleteNote"
and
from django.apps import AppConfig
class LibrarysyncConfig(AppConfig):
name = "LibrarySync"
Django model "doesn"t declare an explicit app_label" __del__: Questions
How can I make a time delay in Python?
5 answers
I would like to know how to put a time delay in a Python script.
Answer #1
import time
time.sleep(5) # Delays for 5 seconds. You can also use a float value.
Here is another example where something is run approximately once a minute:
import time
while True:
print("This prints once a minute.")
time.sleep(60) # Delay for 1 minute (60 seconds).
Answer #2
You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.
from time import sleep
sleep(0.1) # Time in seconds
Django model "doesn"t declare an explicit app_label" __del__: Questions
How to delete a file or folder in Python?
5 answers
How do I delete a file or folder in Python?
Answer #1
os.remove()removes a file.os.rmdir()removes an empty directory.shutil.rmtree()deletes a directory and all its contents.
Path objects from the Python 3.4+ pathlib module also expose these instance methods:
pathlib.Path.unlink()removes a file or symbolic link.pathlib.Path.rmdir()removes an empty directory.
Answer #2
os.remove()removes a file.os.rmdir()removes an empty directory.shutil.rmtree()deletes a directory and all its contents.
Path objects from the Python 3.4+ pathlib module also expose these instance methods:
pathlib.Path.unlink()removes a file or symbolic link.pathlib.Path.rmdir()removes an empty directory.
Answer #3
Python syntax to delete a file
import os
os.remove("/tmp/<file_name>.txt")
Or
import os
os.unlink("/tmp/<file_name>.txt")
Or
pathlib Library for Python version >= 3.4
file_to_rem = pathlib.Path("/tmp/<file_name>.txt")
file_to_rem.unlink()
Path.unlink(missing_ok=False)
Unlink method used to remove the file or the symbolik link.
If missing_ok is false (the default), FileNotFoundError is raised if the path does not exist.
If missing_ok is true, FileNotFoundError exceptions will be ignored (same behavior as the POSIX rm -f command).
Changed in version 3.8: The missing_ok parameter was added.
Best practice
- First, check whether the file or folder exists or not then only delete that file. This can be achieved in two ways :
a.os.path.isfile("/path/to/file")
b. Useexception handling.
EXAMPLE for os.path.isfile
#!/usr/bin/python
import os
myfile="/tmp/foo.txt"
## If file exists, delete it ##
if os.path.isfile(myfile):
os.remove(myfile)
else: ## Show an error ##
print("Error: %s file not found" % myfile)
Exception Handling
#!/usr/bin/python
import os
## Get input ##
myfile= raw_input("Enter file name to delete: ")
## Try to delete the file ##
try:
os.remove(myfile)
except OSError as e: ## if failed, report it back to the user ##
print ("Error: %s - %s." % (e.filename, e.strerror))
RESPECTIVE OUTPUT
Enter file name to delete : demo.txt Error: demo.txt - No such file or directory. Enter file name to delete : rrr.txt Error: rrr.txt - Operation not permitted. Enter file name to delete : foo.txt
Python syntax to delete a folder
shutil.rmtree()
Example for shutil.rmtree()
#!/usr/bin/python
import os
import sys
import shutil
# Get directory name
mydir= raw_input("Enter directory name: ")
## Try to remove tree; if failed show an error using try...except on screen
try:
shutil.rmtree(mydir)
except OSError as e:
print ("Error: %s - %s." % (e.filename, e.strerror))
Is there a simple way to delete a list element by value?
5 answers
I want to remove a value from a list if it exists in the list (which it may not).
a = [1, 2, 3, 4]
b = a.index(6)
del a[b]
print(a)
The above case (in which it does not exist) shows the following error:
Traceback (most recent call last):
File "D:zjm_codea.py", line 6, in <module>
b = a.index(6)
ValueError: list.index(x): x not in list
So I have to do this:
a = [1, 2, 3, 4]
try:
b = a.index(6)
del a[b]
except:
pass
print(a)
But is there not a simpler way to do this?
Answer #1
To remove an element"s first occurrence in a list, simply use list.remove:
>>> a = ["a", "b", "c", "d"]
>>> a.remove("b")
>>> print(a)
["a", "c", "d"]
Mind that it does not remove all occurrences of your element. Use a list comprehension for that.
>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print(a)
[10, 30, 40, 30, 40, 70]
