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In Jinja2, how do you test if a variable is undefined?
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From the Jinja2 template designer documentation:
{% if variable is defined %}
value of variable: {{ variable }}
{% else %}
variable is not defined
{% endif %}
share
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Is 'switch' faster than 'if'?
Is a switch statement actually faster than an if statement?
12 Answers
12
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Fastest way to tell if two files have the same contents in Unix/Linux?
...e same data or not. I do this a for a lot of files, and in my script the diff command seems to be the performance bottleneck.
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How can I check if a Perl array contains a particular value?
... turn the array into a hash:
my %params = map { $_ => 1 } @badparams;
if(exists($params{$someparam})) { ... }
You can also add more (unique) params to the list:
$params{$newparam} = 1;
And later get a list of (unique) params back:
@badparams = keys %params;
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Easy way to test a URL for 404 in PHP?
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If you are using PHP's curl bindings, you can check the error code using curl_getinfo as such:
$handle = curl_init($url);
curl_setopt($handle, CURLOPT_RETURNTRANSFER, TRUE);
/* Get the HTML or whatever is linked in $url. *...
`elif` in list comprehension conditionals
Can we use elif in list comprehension?
6 Answers
6
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How to represent multiple conditions in a shell if statement?
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Classic technique (escape metacharacters):
if [ \( "$g" -eq 1 -a "$c" = "123" \) -o \( "$g" -eq 2 -a "$c" = "456" \) ]
then echo abc
else echo efg
fi
I've enclosed the references to $g in double quotes; that's good practice, in general. Strictly, the parentheses ar...
Check existence of input argument in a Bash shell script
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It is:
if [ $# -eq 0 ]
then
echo "No arguments supplied"
fi
The $# variable will tell you the number of input arguments the script was passed.
Or you can check if an argument is an empty string or not like:
if [ -z "$1" ]
t...
Fixing JavaScript Array functions in Internet Explorer (indexOf, forEach, etc.) [closed]
... to put this in writing. The wiki as a whole is CC Attribution-ShareAlike, if that's an acceptable licence (though CC isn't designed for code as such).
js-methods looks OK in general, but is not as standards-compliant around the edges of how the functions are supposed to be (eg. undefined list item...
One-line list comprehension: if-else variants
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x if y else z is the syntax for the expression you're returning for each element. Thus you need:
[ x if x%2 else x*100 for x in range(1, 10) ]
The confusion arises from the fact you're using a filter in the first example, bu...