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Covariance and contravariance real world example
...iantly as a mammal hat…
IHat<Mammal> mHat = rHat; // Compiler error
// …because…
mHat.hide(new Dolphin()); // Hide a dolphin in a rabbit hat??
// It also cannot be treated contravariantly as a cottontail hat…
IHat<CottonTail> cHat = rHat; // Compiler error
// …becau...
HTML5 Email Validation
...
</form>
And when the user press submit, it automatically shows an error message like:
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How to convert a data frame column to numeric type?
...e" to numeric. If there's just one character element in vector, you'll get error when trying to convert that vector to numerical one.
And just to prove my point:
> err <- c(1, "b", 3, 4, "e")
> mode(err)
[1] "character"
> class(err)
[1] "character"
> char <- as.numeric(err)
Warni...
TypeLoadException says 'no implementation', but it is implemented
I've got a very weird bug on our test machine. The error is:
38 Answers
38
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Format a datetime into a string with milliseconds
...%Y-%m-%d %H:%M:%S.%f')[:-3]
>>>> OUTPUT >>>>
2020-05-04 10:18:32.926
Note: For Python3, print requires parentheses:
print(datetime.utcnow().strftime('%Y-%m-%d %H:%M:%S.%f')[:-3])
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Is there a regular expression to detect a valid regular expression?
...s.
using this with shell script in the grep command , it shows me some error.. grep: Invalid content of {} . I am making a script that could grep a code base to find all the files that contain regular expressions
This pattern exploits an extension called recursive regular expressions. This is ...
Where do “pure virtual function call” crashes come from?
I sometimes notice programs that crash on my computer with the error: "pure virtual function call".
8 Answers
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How to fix “Attempted relative import in non-package” even with __init__.py
...es with py files that have __init__.py files yet you keep getting the ValueError: Attempted relative import in non-package error. I would pay really good money for someone, somewhere, to finally explain in plain English how all of this works.
– AdjunctProfessorFalcon
...
How to list all properties of a PowerShell object
...properties. Note that in the case where you're trying to view a PowerShell error record, you need to use "Format-List * -Force" to truly see all the error information, for example,
$error[0] | Format-List * -force
Note that the wildcard can be used like a traditional wilcard this:
Get-WmiObject ...
how to break the _.each function in underscore.js
...t provide to escape the loop (other than throwing an exception).
However, all hope is not lost! You can use the Array.every method. :)
From that link:
every executes the provided callback function once for each element present in the array until it finds one where callback returns a false valu...