79
votes
When to use a dictionary vs tuple in Python
I would use a namedtuple:
from collections import namedtuple
Filesize = namedtuple('Filesize', 'filename size')
file = Filesize(filename="blabla", size=123)
Now you can use file.size and file....
- 214k
46
votes
Accepted
Why should I use namedtuple over SimpleNamespace when not using dict, they seem very similar
SimpleNamespace is basically just a nice facade on top of a dictionary. It allows you to use properties instead of index keys. This is nice as it is super flexible and easy to manipulate.
The ...
- 7,833
35
votes
Is there a better way to use C# dictionaries than TryGetValue?
Some good answers here on the general principles of hashtables/dictionaries. But I thought I'd touch on your code example,
int x;
if (dict.TryGetValue("key", out x))
{
DoSomethingWith(x);
}
As ...
- 39.5k
30
votes
Accepted
Is there a better way to use C# dictionaries than TryGetValue?
Dictionaries (C# or otherwise) are simply a container where you look up a value based on a key. In many languages it's more correctly identified as a Map with the most common implementation being a ...
- 46.3k
19
votes
When to use a dictionary vs tuple in Python
{"filename": "blabla", "size": 123}, or just ("blabla", 123)
This is the age old question of whether to encode your format / schema in-band or out-of-band.
You trade off some memory to get the ...
- 115k
17
votes
Is there a better way to use C# dictionaries than TryGetValue?
This is neither a code smell nor an anti-pattern, as using TryGet-style functions with an out parameter is idiomatic C#. However, there are 3 options provided in C# to work with a Dictionary, so ...
- 6,130
15
votes
Accepted
Why are there two ways to retrieve values from a dictionary in Python?
Though I was not involved into the design of Python, I think I can make an educated guess:
dictionary["key"]
is shorter and very convenient to use, since it is consistent with access to ...
- 214k
13
votes
Is there a better way to use C# dictionaries than TryGetValue?
There are at least two methods missing from C# dictionaries that in my opinion clean up code considerably in a lot of situations in other languages. The first is returning an Option, which lets you ...
- 148k
10
votes
Why are Python sets and dictionaries not ordered by default?
You are correct that item are store internally with some order, but this internal order is determined by the hash code of the key, which is what allows retrieval to be so fast. So if a set/dict should ...
- 61k
9
votes
Accepted
What is the difference between the solution that uses defaultdict and the one that uses setdefault?
The key line is this one:
d.setdefault(t, []).append(word) return d
d.setdefault is just a function. That function is receiving two arguments: t, and a new list. Both of those arguments are ...
- 206
9
votes
Why are Python sets and dictionaries not ordered by default?
Your premise is incorrect. As of Python 3.6, dicts remember their insertion order. This was an implementation detail, and was promoted to full language feature in 3.7. In 3.6, for the specific case ...
- 2,668
8
votes
Accepted
Why can't Dictionary(TKey, TValue) update it's hashcodes?
Why doesn't the Dictionary class have logic to move an object to the correct bucket when it detects that the object's hashcode has changed?
Just to be sure, we are talking about the hash of the key ...
- 5,493
8
votes
Is there a better way to use C# dictionaries than TryGetValue?
That's 4 lines of code to essentially do the following: DoSomethingWith(dict["key"])
I agree that this is inelegant. A mechanism that I like to use in this case, where the value is a struct ...
- 46.4k
7
votes
When to use a dictionary vs tuple in Python
I would use a class with two properties. file.size is nicer than either file[1] or file["size"].
Simple is better than complex.
- 61k
7
votes
Why is there no key specified with .NET KeyNotFoundException?
This may not be the official answer, but...
C# and VB.NET - the main .NET languages - are statically typed languages(yea, I know, they support dynamic typing, but still). This means properties in ...
- 12.1k
7
votes
Accepted
Do you name a dictionary by the key or the value?
That depends, but generally I'd suggest naming by the values. The keys are often just a way to quickly find what you are actually looking for and will be using.
Depending on context, for your ...
- 409
6
votes
Accepted
Why are Python sets and dictionaries not ordered by default?
The point is not that the overhead is particularly large, more that it is there at all.
Language features must always strike a balance of cost-effectiveness. Dictionaries are absolutely fundamental ...
- 110k
6
votes
Why can't Dictionary(TKey, TValue) update it's hashcodes?
Short answer: Dictionary can't detect that some hashcode changed. There is no event that it can subscribe to. Getting hashcode is just a call to Object.GetHashCode(). That method is called once when ...
- 161
6
votes
Pointers vs keeping indices of objects stored in a central (associative) array?
Is it correct that for the reasons I outlined above avoiding references and embracing ids of objects is considered the preferred approach?
If you want to implement a save button in your game, you ...
- 2,106
6
votes
Query language for python dictionary
Don't eval() unless the user is entirely trusted. Instead, implement a simple language for such conditionals.
For example, we can define a data model that represents the structure of a logical ...
- 135k
5
votes
Why can't Dictionary(TKey, TValue) update it's hashcodes?
If the hash code of the key can change, then the keys can change, and keys that were different can become equal. And now you have a dictionary with equal values and a serious problem.
- 47.5k
5
votes
Why can't Dictionary(TKey, TValue) update it's hashcodes?
Why doesn't the Dictionary class have logic to move an object to the correct bucket when it detects that the object's hashcode has changed?
Because that defeats the object of a dictionary. The whole ...
- 39.5k
5
votes
When to use a dictionary vs tuple in Python
Are the filenames unique? If so, you could scrap the list entirely and just use a pure dictionary for all the files. e.g. (a hypothetical website)
{
"/index.html" : 5467,
"/about.html" : 3425,...
- 8,929
5
votes
Accepted
Is polymorphism appropriate for modeling natural language form (structure), or is there something better?
Completely reviewed answer following the edit of the question.
Linguistic and language processing issues
It would be very challenging to identify common properties and behaviors of adjectives, that ...
- 80.6k
5
votes
Why is there no key specified with .NET KeyNotFoundException?
This question involves digging into the history of .NET Framework design. As such,
People who actually worked in the .NET Framework design team would be able to provide authoritative first-hand ...
- 17k
5
votes
Accepted
What is the space complexity of a Python dictionary?
Space complexity is a property of algorithms, not of data-structures. And your assumption that the dictionary has a (large) fixed size would imply that it is O(1).
It doesn't start with the maximum ...
- 11.6k
5
votes
C# List vs Dictionary cost vs benefit with complex keys
I debated posting this answer because Ewan has good advice, but here goes anyways.
You are over-thinking this.
This is such a small data set that you just need to go with whichever structure meets ...
- 41.9k
5
votes
C# List vs Dictionary cost vs benefit with complex keys
At small sizes of data structures, readability and maintainability of your code is often more important than a minuscule improvement in runtime performance or storage space.
Performance or storage ...
4
votes
Why should I use namedtuple over SimpleNamespace when not using dict, they seem very similar
I really like the answer about structured versus not, so I'm just providing a concrete example below.
SimpleNamespace will accept keys that begin with _. If you're looking for a quick and easy way to ...
- 141
4
votes
Accepted
Dictionary of dictionaries design in C#
There may be a simpler way towards it.
Consider this:
public class NAryDictionary<TKey, TValue> :
Dictionary<TKey, TValue>
{
}
public class NAryDictionary<...
- 888
Only top scored, non community-wiki answers of a minimum length are eligible