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Is there a math nCr function in python? [duplicate]
...
def nCr(n,r):
f = math.factorial
return f(n) / f(r) / f(n-r)
if __name__ == '__main__':
print nCr(4,2)
In Python 3, use the integer division // instead of / to avoid overflows:
return f(n) // f(r) // f(n-r)
Output
6
...
ModelSerializer using model property
...lizer class
class MyModelSerializer(serializers.ModelSerializer):
ext_link = serializers.Field()
class Meta:
model = MyModel
fields = ('name', 'ext_link')
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Getting MAC Address
...inding function into your own code easily:
from uuid import getnode as get_mac
mac = get_mac()
The return value is the mac address as 48 bit integer.
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Does C++ support 'finally' blocks? (And what's this 'RAII' I keep hearing about?)
...ing a mutex:
// A class with implements RAII
class lock
{
mutex &m_;
public:
lock(mutex &m)
: m_(m)
{
m.acquire();
}
~lock()
{
m_.release();
}
};
// A class which uses 'mutex' and 'lock' objects
class foo
{
mutex mutex_; // mutex for l...
Semantic Issue: Property's synthesized getter follows Cocoa naming convention for returning 'owned'
...gs to the none method family as opposed to the new method family:
#ifndef __has_attribute
#define __has_attribute(x) 0 // Compatibility with non-clang compilers
#endif
#if __has_attribute(objc_method_family)
#define BV_OBJC_METHOD_FAMILY_NONE __attribute__((objc_method_family(none)))
#else
#defin...
Regular expression for letters, numbers and - _
...he pattern you want is something like (see it on rubular.com):
^[a-zA-Z0-9_.-]*$
Explanation:
^ is the beginning of the line anchor
$ is the end of the line anchor
[...] is a character class definition
* is "zero-or-more" repetition
Note that the literal dash - is the last character in the ch...
What is a method that can be used to increment letters?
...chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ') {
this._chars = chars;
this._nextId = [0];
}
next() {
const r = [];
for (const char of this._nextId) {
r.unshift(this._chars[char]);
}
this._increment();
return r.join('');
}
_increment() {
...
MongoDB SELECT COUNT GROUP BY
...ier way to do it using aggregate:
db.contest.aggregate([
{"$group" : {_id:"$province", count:{$sum:1}}}
])
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Loop through files in a directory using PowerShell
...eived Files" -Filter *.log |
Foreach-Object {
$content = Get-Content $_.FullName
#filter and save content to the original file
$content | Where-Object {$_ -match 'step[49]'} | Set-Content $_.FullName
#filter and save content to a new file
$content | Where-Object {$_ -match 's...
Regex Named Groups in Java
...> TEST
matcher.name(1) ==> login
Replace
matcher.replaceAll("aaaaa_$1_sssss_$2____") ==> aaaaa_TEST_sssss_123____
matcher.replaceAll("aaaaa_${login}_sssss_${id}____") ==> aaaaa_TEST_sssss_123____
(extract from the implementation)
public final class Pattern
implements java.io...