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Check if OneToOneField is None in Django
...elect_related() now or in the future -- or maybe even to be sure you also handle other sorts of magic which may happen elsewhere -- you have to extend the test as follows: if hasattr(object, 'onetoonerevrelattr') and object.onetoonerevrelattr != None
– class stacker
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Is there a way to include commas in CSV columns without breaking the formatting?
I've got a two column CSV with a name and a number. Some people's name use commas, for example Joe Blow, CFA. This comma breaks the CSV format, since it's interpreted as a new column.
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Print string to text file
...ext_file.write("Purchase Amount: {0}".format(TotalAmount))
For python2.7 and higher you can use {} instead of {0}
In Python3, there is an optional file parameter to the print function
with open("Output.txt", "w") as text_file:
print("Purchase Amount: {}".format(TotalAmount), file=text_file)
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How to list running screen sessions?
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To list all of the screen sessions for a user, run the following command as that user:
screen -ls
To see all screen sessions on a specific machine you can do:
ls -laR /var/run/screen/
I get this on my machine:
gentle ~ # ls -laR /var/run/screen/
/var/run/screen/:
total 1
drwxrwxr-x 4 ...
Determine on iPhone if user has enabled push notifications
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Call enabledRemoteNotificationsTypes and check the mask.
For example:
UIRemoteNotificationType types = [[UIApplication sharedApplication] enabledRemoteNotificationTypes];
if (types == UIRemoteNotificationTypeNone)
// blah blah blah
iOS8 and above:
[[U...
Listing only directories using ls in Bash?
This command lists directories in the current path: ls -d */
26 Answers
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How can I remove non-ASCII characters but leave periods and spaces using Python?
...rom the file with no non-ASCII characters. However, I want to leave spaces and periods. At present, I'm stripping those too. Here's the code:
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Save all files in Visual Studio project as UTF-8
... into a specific character encoding. I got a solution with mixed encodings and I want to make them all the same (UTF-8 with signature).
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Regex empty string or email
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This regex pattern will match an empty string:
^$
And this will match (crudely) an email or an empty string:
(^$|^.*@.*\..*$)
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Python: List vs Dict for look up table
...f you don't need to associate values, use sets.
Memory
Both dictionaries and sets use hashing and they use much more memory than only for object storage. According to A.M. Kuchling in Beautiful Code, the implementation tries to keep the hash 2/3 full, so you might waste quite some memory.
If you...