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Hidden features of Perl?
...cumented somewhere, or follow logically from the documented features, but nonetheless some are not very well known.
Update: Another nice one. Below the q{...} quoting constructs were mentioned, but did you know that you can use letters as delimiters?
$ perl -Mstrict -wle 'print q bJet another per...
python date of the previous month
...h, then do it again to get the day you want. First: d = date.today() then one_month_ago = (d.replace(day=1) - timedelta(days=1)).replace(day=d.day)
– Thane Plummer
Jul 15 '15 at 22:12
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Singleton: How should it be used
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Answer:
Use a Singleton if:
You need to have one and only one object of a type in system
Do not use a Singleton if:
You want to save memory
You want to try something new
You want to show off how much you know
Because everyone else is doing it (See cargo cult programme...
Are duplicate keys allowed in the definition of binary search trees?
...airly trivial to implement duplicates (either as a list at the node, or in one particular direction.)
Most (that I've seen) specify left children as <= and right children as >. Practically speaking, a BST which allows either of the right or left children to be equal to the root node, will re...
Compile time string hashing
...might be possible to compute a string's hash at compile time. However, no one seems to be ready to come out and say that it will be possible or how it would be done.
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Difference between two lists
...ated they want "Items who are in the first without the items in the second one" - that sounds like a set difference to me. If the first list contains { 5, 5, 5, 5, 1 } and the second list contains { 5 } then only 1 is in the first list but not the second.
– Jon Skeet
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How to get all possible combinations of a list’s elements?
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This answer missed one aspect: the OP asked for ALL combinations... not just combinations of length "r".
So you'd either have to loop through all lengths "L":
import itertools
stuff = [1, 2, 3]
for L in range(0, len(stuff)+1):
for subset...
Thread vs ThreadPool
...e there and why should I consider using a thread from the pool rather than one I've explicitly created? I'm thinking specifically of .NET here, but general examples are fine.
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Is it fine to have foreign key as primary key?
...) to act as the primary key.
The only exception to this are tables with a one-to-one relationship, where the foreign key and primary key of the linked table are one and the same.
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Bash continuation lines
...ntinuation lines
If this creates two arguments to echo and you only want one, then let's look at string concatenation. In bash, placing two strings next to each other concatenate:
$ echo "continuation""lines"
continuationlines
So a continuation line without an indent is one way to break up a s...