Maps in Prolog

Based on the input provided, the target language for the translation is Python. Below is the translation of the Go code example into Python, along with the explanation in Markdown format suitable for Hugo.

Maps#

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

To create an empty dictionary, use the builtin dict().

# Create an empty dictionary
m = dict()

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

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

Printing a dictionary with e.g. 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, accessing it directly will raise a KeyError. You can use the get method which returns None (or a specified default) if the key is not found.

v3 = m.get("k3", 0)
print("v3:", v3)

The builtin len returns the number of key/value pairs when called on a dictionary.

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

To remove key/value pairs from a dictionary, use the del statement.

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

To remove all key/value pairs from a dictionary, use the clear method.

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

You can also check if a key is present in the dictionary using the in keyword.

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

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

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

Note that dictionaries appear in the form {k: v, k: v} when printed with print().

# Run the Python script
$ python maps.py 
map: {'k1': 7, 'k2': 13}
v1: 7
v3: 0
len: 2
map: {'k1': 7}
map: {}
prs: False
map: {'foo': 1, 'bar': 2}

Next example: Functions.