Maps in D Programming Language

The selected target language is Python. Here’s the translated code and explanation:

Maps are Python’s built-in associative data type (sometimes called dictionaries or hashes in other languages).

To create an empty map, use the built-in dict constructor:

m = {}

Set key/value pairs using the typical name[key] = val syntax.

m["k1"] = 7
m["k2"] = 13

Printing a map with print will show all of its key/value pairs.

print("map:", m)

Get a value for a key with name[key].

v1 = m["k1"]
print("v1:", v1)

If the key doesn’t exist, attempting to access it with name[key] will raise a KeyError. A safer way to get a value is to use the get method, which returns None if the key does not exist.

v3 = m.get("k3", 0)  # You can provide a default value
print("v3:", v3)

The built-in len function returns the number of key/value pairs in a dictionary.

print("len:", len(m))

The built-in del statement removes key/value pairs from a map.

del m["k2"]
print("map:", m)

To remove all key/value pairs from a map, you can use the clear method.

m.clear()
print("map:", m)

The optional second return value when getting a value from a map indicates if the key was present in the map. This can be used to disambiguate between missing keys and keys with zero values like 0 or "".

Here’s how you can check for the presence of a key:

prs = "k2" in m
print("prs:", prs)

You can also declare and initialize a new map in the same line with this syntax.

n = {"foo": 1, "bar": 2}
print("map:", n)

Python’s assert statement is useful for testing if two dictionaries are equal.

n2 = {"foo": 1, "bar": 2}
if n == n2:
    print("n == n2")

Note that maps appear in the form {'k': 'v', 'k': 'v'} when printed with print.

$ python3 maps.py
map: {'k1': 7, 'k2': 13}
v1: 7
v3: 0
len: 2
map: {'k1': 7}
map: {}
prs: False
map: {'foo': 1, 'bar': 2}
n == n2

Next example: Functions.