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How to check whether a file or directory exists?
...iven file or directory exists
func exists(path string) (bool, error) {
_, err := os.Stat(path)
if err == nil { return true, nil }
if os.IsNotExist(err) { return false, nil }
return false, err
}
Edited to add error handling.
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How do I create a MongoDB dump of my database?
...ump:
$ ./mongodump --host prod.example.com
connected to: prod.example.com
all dbs
DATABASE: log to dump/log
log.errors to dump/log/errors.bson
713 objects
log.analytics to dump/log/analytics.bson
234810 objects
DATABASE: blog to dump/blog
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What is the difference between __init__ and __call__?
I want to know the difference between __init__ and __call__ methods.
13 Answers
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How to search a Git repository by commit message?
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To search the commit log (across all branches) for the given text:
git log --all --grep='Build 0051'
To search the actual content of commits through a repo's history, use:
git grep 'Build 0051' $(git rev-list --all)
to show all instances of the given t...
How to prevent ifelse() from turning Date objects into numeric objects
...irst this felt a little "hackish" to me. But now I just think of it as a small price to pay for the performance returns that I get from ifelse(). Plus it's still a lot more concise than a loop.
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Setting a property by reflection with a string value
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You can use Convert.ChangeType() - It allows you to use runtime information on any IConvertible type to change representation formats. Not all conversions are possible, though, and you may need to write special case logic if you want to support conversions from t...
What is a “callback” in C and how are they implemented?
...y're implemented using function pointers. Here's an example:
void populate_array(int *array, size_t arraySize, int (*getNextValue)(void))
{
for (size_t i=0; i<arraySize; i++)
array[i] = getNextValue();
}
int getNextRandomValue(void)
{
return rand();
}
int main(void)
{
int m...
Modular multiplicative inverse function in Python
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If you happen to be using sympy, then x, _, g = sympy.numbers.igcdex(a, m) does the trick.
– Lynn
Sep 16 '16 at 18:15
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Get keys from HashMap in Java
...HashMap contains more than one key. You can use keySet() to get the set of all keys.
team1.put("foo", 1);
team1.put("bar", 2);
will store 1 with key "foo" and 2 with key "bar". To iterate over all the keys:
for ( String key : team1.keySet() ) {
System.out.println( key );
}
will print "foo"...
How to initialize std::vector from C-style array?
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Don't forget that you can treat pointers as iterators:
w_.assign(w, w + len);
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