Here’s one way to do it: if not any(d[‘main_color’] == ‘red’ for d in a): # does not exist The part in parentheses is a generator expression that returns True for each dictionary that has the key-value pair you are looking for, otherwise False. If the key could also be missing the above code can … Read more
If you have another variable also referring to the same dictionary, there is a big difference: >>> d = {“stuff”: “things”} >>> d2 = d >>> d = {} >>> d2 {‘stuff’: ‘things’} >>> d = {“stuff”: “things”} >>> d2 = d >>> d.clear() >>> d2 {} This is because assigning d = {} creates … Read more
In Java 8, use Map.getOrDefault. It takes the key, and the value to return if no matching key is found.
Dictionary views are essentially what their name says: views are simply like a window on the keys and values (or items) of a dictionary. Here is an excerpt from the official documentation for Python 3: >>> dishes = {‘eggs’: 2, ‘sausage’: 1, ‘bacon’: 1, ‘spam’: 500} >>> keys = dishes.keys() >>> values = dishes.values() >>> # … Read more
dict((el,0) for el in a) will work well. Python 2.7 and above also support dict comprehensions. That syntax is {el:0 for el in a}.
Call list() on the dictionary instead: keys = list(test) In Python 3, the dict.keys() method returns a dictionary view object, which acts as a set. Iterating over the dictionary directly also yields keys, so turning a dictionary into a list results in a list of all the keys: >>> test = {‘foo’: ‘bar’, ‘hello’: ‘world’} … Read more
Python’s mostly implementing a pragmatically tinged flavor of command-query separation: mutators return None (with pragmatically induced exceptions such as pop😉 so they can’t possibly be confused with accessors (and in the same vein, assignment is not an expression, the statement-expression separation is there, and so forth). That doesn’t mean there aren’t a lot of ways … Read more
.NET 4.5 The .NET Framework 4.5 BCL introduces ReadOnlyDictionary<TKey, TValue> (source). As the .NET Framework 4.5 BCL doesn’t include an AsReadOnly for dictionaries, you will need to write your own (if you want it). It would be something like the following, the simplicity of which perhaps highlights why it wasn’t a priority for .NET 4.5. … Read more
This is safe! You can also find a similar sample in Effective Go: for key := range m { if key.expired() { delete(m, key) } } And the language specification: The iteration order over maps is not specified and is not guaranteed to be the same from one iteration to the next. If map entries … Read more
You can define += operator for Dictionary, e.g., func += <K, V> (left: inout [K:V], right: [K:V]) { for (k, v) in right { left[k] = v } }