Szathmáry László honlapja @ DEIK | DLang / Create a dictionary; read/write

Dictionaries in D are unordered collections.

(1) create a dictionary; read/write
def main(): # d: dict[int, str] = {} d = {} d[1] = "one" d[3] = "three" print(d) # {1: 'one', 3: 'three'} d2 = { 1: "one", 3: "three" } print(d2) # {1: 'one', 3: 'three'} # print a value print(d[1]) # one	import std.stdio; void main() { string[int] d; // order: value[key] d[1] = "one"; d[3] = "three"; writeln(d); // [3:"three", 1:"one"] auto d2 = [ 1: "one", 3: "three" ]; writeln(d2); // [3:"three", 1:"one"] // print a value writeln(d[1]); // one }
def main(): d = {} d[1] = ["one", "egy"] d[2] = ["two", "kettő"] d[3] = ["three", "három"] print(d) """ {1: ['one', 'egy'], 2: ['two', 'kettő'], 3: ['three', 'három']} """	import std.stdio; void main() { string[][int] d; d[1] = ["one", "egy"]; d[2] = ["two", "kettő"]; d[3] = ["three", "három"]; writeln(d); /* [3:["three", "három"], 2:["two", "kettő"], 1:["one", "egy"]] */ }

Notice that when you specify the type of a dictionary, then the order is a bit strange: value_type[key_type]. Well, when you want to access a value, we use this syntax: writeln(d[1]);, i.e. we indicate the key between the square brackets.

Passint a dictionary to a function

(2) passing to a function
def modify(d: dict) -> None: d[2] = "two" def main(): d = {} d[1] = "one" d[3] = "three" print(d) # {1: 'one', 3: 'three'} modify(d) print(d) # {1: 'one', 3: 'three', 2: 'two'}	import std.stdio; void modify(string[int] d) { d[2] = "two"; } void main() { string[int] d; d[1] = "one"; d[3] = "three"; writeln(d); // [3:"three", 1:"one"] modify(d); writeln(d); // [3:"three", 2:"two", 1:"one"] }

It behaves just like in Python. d is an object (a reference pointing on an object), and thus the object is passed by reference. If you change the dictionary in a function, the caller will see the changes.

Remove an element; remove all elements

(3) remove element(s)
def main(): d = {} d[1] = "one" d[2] = "two" d[3] = "three" print(d) # {1: 'one', 2: 'two', 3: 'three'} del d[2] print(d) # {1: 'one', 3: 'three'} # del d[2] # KeyError exception, no such key d.clear() print(d) # {}	import std.stdio; void main() { string[int] d; d[1] = "one"; d[2] = "two"; d[3] = "three"; writeln(d); // [3:"three", 2:"two", 1:"one"] d.remove(2); // returns true, key found writeln(d); // [3:"three", 1:"one"] d.remove(2); // returns false, no such key writeln(d); // [3:"three", 1:"one"] d.clear(); writeln(d); // [] }

In Python, when you want to remove an element by using a non-existing key, you get an error. In D, the function remove() returns false in this case.

The `in` operator

(4) in
def main(): d = {} d[1] = "one" d[2] = "two" d[3] = "three" print(d) # {1: 'one', 2: 'two', 3: 'three'} if 2 in d: print("2 was found") # will be printed if 9 not in d: print("9 was not found") # will be printed	import std.stdio; void main() { string[int] d; d[1] = "one"; d[2] = "two"; d[3] = "three"; writeln(d); // [3:"three", 2:"two", 1:"one"] if (2 in d) { writeln("2 was found"); // will be printed } if (9 !in d) { writeln("9 was not found"); // will be printed } }

The `get()` function

(5) `get()`
def main(): d = {} d[1] = "one" d[2] = "two" d[3] = "three" print(d) # {1: 'one', 2: 'two', 3: 'three'} # print(d[9]) # KeyError, no such key print(d.get(9)) # None print(d.get(9, "not found")) # "not found"	import std.stdio; void main() { string[int] d; d[1] = "one"; d[2] = "two"; d[3] = "three"; writeln(d); // [3:"three", 2:"two", 1:"one"] // writeln(d[9]); // error, no such key // writeln(d.get(9)); // error, no such function // a default value MUST be provided writeln(d.get(9, "not found")); // "not found" }

Length, keys, values

(6) length, keys, values

def main():
d = {}
d[1] = "one"
d[2] = "two"
d[3] = "three"
print(d) # {1: 'one', 2: 'two', 3: 'three'}

# 1
print(len(d)) # 3, number of key/value pairs

# 2
key_list = list(d.keys())
print(key_list) # [1, 2, 3]

# 3
value_list = list(d.values())
print(value_list) # ['one', 'two', 'three']

# 4
for k in d.keys(): # loop over an iterator
print(k)

# 5
for k in d: # same as before (loop over the keys)
print(k)

# 6
for v in d.values(): # loop over an iterator
print(v)

# 7
for k, v in d.items(): # loop over an iterator
print(k, "->", v)

import std.stdio;

void main()
{
string[int] d;
d[1] = "one";
d[2] = "two";
d[3] = "three";
writeln(d); // [3:"three", 2:"two", 1:"one"]

// 1
writeln(d.length); // 3, number of key/value pairs

// 2
writeln(d.keys()); // [3, 2, 1], as list

// 3
writeln(d.values()); // ["three", "two", "one"], as list

// 4; no list is created; we loop over a range
foreach (k; d.byKey) {
writeln(k);
}

// 5; !!! it iterates over the VALUES !!!
foreach (v; d) {
writeln(v);
}

// 6; no list is created; we loop over a range
foreach (v; d.byValue) {
writeln(v);
}

// 7a
foreach (k, v; d) {
writeln(k, " -> ", v);
}

// 7b; unpacking doesn't work here
foreach (pair; d.byKeyValue) {
writeln(pair.key, " -> ", pair.value);
}
}

The by*() functions return a range, not a list.

Create a dictionary; read/write

Passint a dictionary to a function

Remove an element; remove all elements

The in operator

The get() function

Length, keys, values

The `in` operator

The `get()` function