The snippets are under the CC-BY-SA license. # Programming-Idioms.org

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1
Print a literal string on standard output
``print("Hello World")``
Alternative implementation:
``print('Hello World')``
``println!("Hello World");``
2
Loop to execute some code a constant number of times
``````for _ in range(10):
print("Hello")``````
Alternative implementation:
``print("Hello\n"*10)``
Alternative implementation:
``````i = 0
while i < 10:
print('hello')
i = i + 1``````
``for _ in 0..10 { println!("Hello"); }``
Alternative implementation:
``print!("{}", "Hello\n".repeat(10));``
3
Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)
``````def finish(name):
print(f'My job here is done. Goodbye {name}')``````
``````fn finish(name: &str) {
println!("My job here is done. Goodbye {}", name);
}``````
4
Create a function which returns the square of an integer
``````def square(x):
return x*x``````
Alternative implementation:
``````def square(x):
return x**2``````
``fn square(x : u32) -> u32 { x * x }``
5
Declare a container type for two floating-point numbers x and y
``````@dataclass
class Point:
x: float
y: float``````
Alternative implementation:
``Point = namedtuple("Point", "x y")``
``````struct Point {
x: f64,
y: f64,
}``````
Alternative implementation:
``struct Point(f64, f64);``
6
Do something with each item x of the list (or array) items, regardless indexes.
``````for x in items:
doSomething( x )``````
Alternative implementation:
``[do_something(x) for x in items]``
``````for x in items {
do_something(x);
}``````
Alternative implementation:
``items.into_iter().for_each(|x| do_something(x));``
7
Print each index i with its value x from an array-like collection items
``````for i, x in enumerate(items):
print(i, x)``````
``````for (i, x) in items.iter().enumerate() {
println!("Item {} = {}", i, x);
}``````
Alternative implementation:
``````items.iter().enumerate().for_each(|(i, x)| {
println!("Item {} = {}", i, x);
})``````
8
Create a new map object x, and provide some (key, value) pairs as initial content.
``x = {"one" : 1, "two" : 2}``
``````let mut x = BTreeMap::new();
x.insert("one", 1);
x.insert("two", 2);``````
Alternative implementation:
``````let x: HashMap<&str, i32> = [
("one", 1),
("two", 2),
].into_iter().collect();``````
9
The structure must be recursive because left child and right child are binary trees too. A node has access to children nodes, but not to its parent.
``````class Node:
def __init__(self, data):
self.data = data
self.left = None
self.right = None``````
Alternative implementation:
``````class Node:
def __init__(self, data, left_child, right_child):
self.data = data
self._left_child = left_child
self._right_child = right_child``````
``````struct BinTree<T> {
value: T,
left: Option<Box<BinTree<T>>>,
right: Option<Box<BinTree<T>>>,
}``````
10
Generate a random permutation of the elements of list x
``shuffle(x)``
Alternative implementation:
``random.shuffle(x)``
``````let mut rng = StdRng::new().unwrap();
rng.shuffle(&mut x);``````
Alternative implementation:
``````let mut rng = thread_rng();
x.shuffle(&mut rng);``````
11
The list x must be non-empty.
``random.choice(x)``
``x[rand::thread_rng().gen_range(0..x.len())]``
Alternative implementation:
``````let mut rng = rand::thread_rng();
let choice = x.choose(&mut rng).unwrap();``````
12
Check if the list contains the value x.
list is an iterable finite container.
``x in list``
``list.contains(&x);``
Alternative implementation:
``list.iter().any(|v| v == &x)``
Alternative implementation:
``(&list).into_iter().any(|v| v == &x)``
Alternative implementation:
``list.binary_search(&x).is_ok()``
13
Access each key k with its value x from an associative array mymap, and print them.
``````for k, v in mymap.items():
print(k, v)``````
``````for (k, x) in &mymap {
println!("Key={key}, Value={val}", key=k, val=x);
}``````
14
Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b.
``random.uniform(a,b)``
``thread_rng().gen_range(a..b);``
15
Pick a random integer greater than or equals to a, inferior or equals to b. Precondition : a < b.
``random.randint(a,b)``
``````fn pick(a: i32, b: i32) -> i32 {
let between = Range::new(a, b);
between.ind_sample(&mut rng)
}
``````
Alternative implementation:
``Uniform::new_inclusive(a, b).sample(&mut rand::thread_rng())``
16
Call a function f on every node of binary tree bt, in depth-first infix order
``````def dfs(bt):
if bt is None:
return
dfs(bt.left)
f(bt)
dfs(bt.right)``````
``````fn depthFirstTraverse<T>(bt: &mut BiTree<T>, f: fn(&mut BiTree<T>)) {
if let Some(left) = &mut bt.left {
f(left);
}

f(bt);

if let Some(right) = &mut bt.right {
f(right);
}
}``````
17
The structure must be recursive. A node may have zero or more children. A node has access to its children nodes, but not to its parent.
``````class Node:
def __init__(self, value, *children):
self.value = value
self.children = list(children)``````
``````struct Node<T> {
value: T,
children: Vec<Node<T>>,
}``````
18
Call a function f on every node of a tree, in depth-first prefix order
``````def DFS(f, root):
f(root)
for child in root:
DFS(f, child)``````
``````pub struct Tree<V> {
children: Vec<Tree<V>>,
value: V
}

impl<V> Tree<V> {
pub fn dfs<F: Fn(&V)>(&self, f: F) {
self.dfs_helper(&f);
}
fn dfs_helper<F: Fn(&V)>(&self, f: &F) {
(f)(&self.value);
for child in &self.children {
child.dfs_helper(f)
}
}
// ...
}``````
19
Reverse the order of the elements of the list x.
This may reverse "in-place" and destroy the original ordering.
``x = reversed(x)``
Alternative implementation:
``y = x[::-1]``
Alternative implementation:
``x.reverse()``
``let y: Vec<_> = x.into_iter().rev().collect();``
Alternative implementation:
``x.reverse();``
20
Implement a function search which looks for item x in a 2D matrix m.
Return indices i, j of the matching cell.
Think of the most idiomatic way in the language to return the two values at the same time.
``````def search(m, x):
for idx, item in enumerate(m):
if x in item:
return idx, item.index(x)``````
``````fn search<T: Eq>(m: &Vec<Vec<T>>, x: &T) -> Option<(usize, usize)> {
for (i, row) in m.iter().enumerate() {
for (j, column) in row.iter().enumerate() {
if *column == *x {
return Some((i, j));
}
}
}

None
}``````
21
Swap the values of the variables a and b
``a, b = b, a``
Alternative implementation:
``````a =int(input("enter a number"))
b =int(input("enter b number"))
a, b = b, a

print("Value of a:", a)
print("Value of a", b)
``````
``````std::mem::swap(&mut a, &mut b);
``````
Alternative implementation:
``let (a, b) = (b, a);``
22
Extract the integer value i from its string representation s (in radix 10)
``i = int(s)``
``let i = s.parse::<i32>().unwrap();``
Alternative implementation:
``let i: i32 = s.parse().unwrap_or(0);``
Alternative implementation:
``````let i = match s.parse::<i32>() {
Ok(i) => i,
Err(_e) => -1,
};``````
23
Given a real number x, create its string representation s with 2 decimal digits following the dot.
``s =  '{:.2f}'.format(x)``
Alternative implementation:
``s = f'{x:.2f}'``
``let s = format!("{:.2}", x);``
24
Declare a new string s and initialize it with the literal value "ネコ" (which means "cat" in japanese)
``s = "ネコ"``
``let s = "ネコ";``
25
Share the string value "Alan" with an existing running process which will then display "Hello, Alan"
``````q = Queue()

def worker():
while True:
print(f"Hello, {q.get()}")

q.put("Alan")
q.join()``````
``````let (send, recv) = channel();

loop {
let msg = recv.recv().unwrap();
println!("Hello, {:?}", msg);
}
});

send.send("Alan").unwrap();``````
26
Declare and initialize a matrix x having m rows and n columns, containing real numbers.
``x = [ * n for _ in range(m)]``
``let mut x = vec![vec![0.0f64; N]; M];``
Alternative implementation:
``let mut x = [[0.0; N] ; M];``
27
Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers.
``x = [[[0 for k in range(p)] for j in range(n)] for i in range(m)]``
Alternative implementation:
``x = numpy.zeros((m,n,p))``
``let x = vec![vec![vec![0.0f64; p]; n]; m];``
Alternative implementation:
``let x = [[[0.0f64; P]; N]; M];``
28
Sort the elements of the list (or array-like collection) items in ascending order of x.p, where p is a field of the type Item of the objects in items.
``items = sorted(items, key=lambda x: x.p)``
Alternative implementation:
``items = sorted(items, key=attrgetter('p'))``
``items.sort_by(|a,b| a.p.cmp(&b.p));``
Alternative implementation:
``items.sort_by_key(|x| x.p);``
29
Remove i-th item from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
Note that in most languages, the smallest valid value for i is 0.
``del items[i]``
Alternative implementation:
``items.pop(i)``
``items.remove(i)``
30
Launch the concurrent execution of procedure f with parameter i from 1 to 1000.
Tasks are independent and f(i) doesn't return any value.
Tasks need not run all at the same time, so you may use a pool.
``````pool = Pool()
for i in range(1, 1001):
pool.apply_async(f, [i])``````
``````let threads: Vec<_> = (0..1000).map(|i| {
}).collect();

}``````
Alternative implementation:
``(0..1000).into_par_iter().for_each(f);``
31
Create the recursive function f which returns the factorial of the non-negative integer i, calculated from f(i-1)
``````def f(i):
if i == 0:
return 1
else:
return i * f(i-1)``````
``````fn f(n: u32) -> u32 {
if n < 2 {
1
} else {
n * f(n - 1)
}
}``````
Alternative implementation:
``````fn factorial(num: u64) -> u64 {
match num {
0 | 1 => 1,
_ => factorial(num - 1) * num,
}
}``````
32
Create function exp which calculates (fast) the value x power n.
x and n are non-negative integers.
``````def exp(x, n):
return x**n
``````
``````fn exp(x: u64, n: u64) -> u64 {
match n {
0 => 1,
1 => x,
i if i % 2 == 0 => exp(x * x, n / 2),
_ => x * exp(x * x, (n - 1) / 2),
}
}``````
Alternative implementation:
``````fn exp(x: u64, n: u32) -> u64 {
x.pow(n)
}``````
33
Assign to the variable x the new value f(x), making sure that no other thread may modify x between the read and the write.
``````lock = threading.Lock()

lock.acquire()
try:
x = f(x)
finally:
lock.release()``````
Alternative implementation:
``````with threading.Lock():
x = f(x)
``````
``````let mut x = x.lock().unwrap();
*x = f(x);``````
34
Declare and initialize a set x containing unique objects of type T.
``````class T(object):
pass

x = set(T())``````
Alternative implementation:
``````class T:
...

s = set(T() for _ in range(x))``````
``let x: HashSet<T> = HashSet::new();``
35
Implement a function compose (A -> C) with parameters f (A -> B) and g (B -> C), which returns the composition function g ∘ f
``````def compose(f, g):
return lambda a: g(f(a))``````
``````fn compose<'a, A, B, C, G, F>(f: F, g: G) -> Box<Fn(A) -> C + 'a>
where F: 'a + Fn(A) -> B, G: 'a + Fn(B) -> C
{
Box::new(move |x| g(f(x)))
}``````
Alternative implementation:
``````fn compose<A, B, C>(f: impl Fn(A) -> B, g: impl Fn(B) -> C) -> impl Fn(A) -> C {
move |x| g(f(x))
}``````
36
Implement a function compose which returns composition function g ∘ f for any functions f and g having exactly 1 parameter.
``````def compose(f, g):
return lambda x: g(f(x))``````
``````fn compose<'a, A, B, C, G, F>(f: F, g: G) -> Box<Fn(A) -> C + 'a>
where F: 'a + Fn(A) -> B, G: 'a + Fn(B) -> C
{
Box::new(move |x| g(f(x)))
}``````
Alternative implementation:
``````fn compose<A, B, C>(f: impl Fn(A) -> B, g: impl Fn(B) -> C) -> impl Fn(A) -> C {
move |x| g(f(x))
}``````
37
Transform a function that takes multiple arguments into a function for which some of the arguments are preset.
``````def add(a, b):
return a+b

``````fn add(a: u32, b: u32) -> u32 {
a + b
}

``````
38
Find substring t consisting in characters i (included) to j (excluded) of string s.
Character indices start at 0 unless specified otherwise.
Make sure that multibyte characters are properly handled.
``t = s[i:j]``
``let t = s.graphemes(true).skip(i).take(j - i).collect::<String>();``
Alternative implementation:
``let t = s.substring(i, j);``
39
Set the boolean ok to true if the string word is contained in string s as a substring, or to false otherwise.
``ok = word in s``
``let ok = s.contains(word);``
40
Declare a Graph data structure in which each Vertex has a collection of its neighbouring vertices.
``````class Vertex(set): pass
class Graph(defaultdict):
def __init__(self, *paths):
self.default_factory = Vertex
for path in paths:
self.make_path(path)

def make_path(self, labels):
for l1, l2 in zip(labels, labels[1:]):

G = Graph((0, 1, 2, 3), (1, 4, 2))``````
41
Create string t containing the same characters as string s, in reverse order.
Original string s must remain unaltered. Each character must be handled correctly regardless its number of bytes in memory.
``t = s.decode('utf8')[::-1].encode('utf8')``
Alternative implementation:
``t = s[::-1]``
``let t = s.chars().rev().collect::<String>();``
Alternative implementation:
``let t: String = s.chars().rev().collect();``
42
Print each item v of list a which is not contained in list b.
For this, write an outer loop to iterate on a and an inner loop to iterate on b.
``````for v in a:
try:
for u in b:
if v == u:
raise Exception()
print(v)
except Exception:
continue
``````
Alternative implementation:
``````for v in a:
keep = True
for w in b:
if w == v:
keep = False
break
if keep:
print(v)``````
``````'outer: for va in &a {
for vb in &b {
if va == vb {
continue 'outer;
}
}
println!("{}", va);
}
``````
43
Look for a negative value v in 2D integer matrix m. Print it and stop searching.
``````class BreakOuterLoop (Exception): pass

try:
position = None
for row in m:
for column in m[row]:
if m[row][column] == v:
position = (row, column)
raise BreakOuterLoop
except BreakOuterLoop:
pass``````
Alternative implementation:
``````def loop_breaking(m, v):
for i, row in enumerate(m):
for j, value in enumerate(row):
if value == v:
return (i, j)
return None

print(loop_breaking(([1,2,3],[4,5,6],[7,8,9]), 6))``````
Alternative implementation:
``````matrix = [[1,2,3],[4,-5,6],[7,8,9]]
try:
print(next(i for i in chain.from_iterable(matrix) if i < 0))
except StopIteration:
pass``````
``````'outer: for v in m {
'inner: for i in v {
if i < 0 {
println!("Found {}", i);
break 'outer;
}
}
}``````
44
Insert the element x at position i in the list s. Further elements must be shifted to the right.
``s.insert(i, x)``
``s.insert(i, x);``
45
Sleep for 5 seconds in current thread, before proceeding with the next instructions.
``time.sleep(5)``
``thread::sleep(time::Duration::from_secs(5));``
46
Create string t consisting of the 5 first characters of string s.
Make sure that multibyte characters are properly handled.
``t = s[:5]``
``let t = s.char_indices().nth(5).map_or(s, |(i, _)| &s[..i]);``
Alternative implementation:
``let t = s.chars().take(5).collect::<String>();``
47
Create string t consisting in the 5 last characters of string s.
Make sure that multibyte characters are properly handled.
``t = s[-5:]``
``````let last5ch = s.chars().count() - 5;
let t: String = s.chars().skip(last5ch).collect();
``````
48
Assign to variable s a string literal consisting in several lines of text, including newlines.
``````s = """Huey
Dewey
Louie"""``````
``````let s = "line 1
line 2
line 3";``````
Alternative implementation:
``````let s = r#"Huey
Dewey
Louie"#;``````
49
Build list chunks consisting in substrings of the string s, separated by one or more space characters.
``chunks = s.split()``
``let chunks: Vec<_> = s.split_whitespace().collect();``
Alternative implementation:
``let chunks: Vec<_> = s.split_ascii_whitespace().collect();``
Alternative implementation:
``let chunks: Vec<_> = s.split(' ').collect();``
50
Write a loop that has no end clause.
``````while True:
pass``````
``````loop {
// Do something
}``````
51
Determine whether the map m contains an entry for the key k
``k in m``
``m.contains_key(&k)``
52
Determine whether the map m contains an entry with the value v, for some key.
``v in m.values()``
``let does_contain = m.values().any(|&val| *val == v);``
53
Concatenate elements of string list x joined by the separator ", " to create a single string y.
``````y = ', '.join(x)
``````
Alternative implementation:
``y = ', '.join(map(str, x))``
``let y = x.join(", ");``
54
Calculate the sum s of the integer list or array x.
``s = sum(x)``
``x.iter().sum()``
Alternative implementation:
``let s = x.iter().sum::<i32>();``
55
Create the string representation s (in radix 10) of the integer value i.
``s = str(i)``
``let s = i.to_string();``
Alternative implementation:
``let s = format!("{}", i);``
56
Fork-join : launch the concurrent execution of procedure f with parameter i from 1 to 1000.
Tasks are independent and f(i) doesn't return any value.
Tasks need not run all at the same time, so you may use a pool.
Wait for the completion of the 1000 tasks and then print "Finished".
``````def f(i):
i * i

with Pool(1000) as p:
p.map(func=f, iterable=range(1, 1001))

print('Finished')``````
``````let threads: Vec<_> = (0..1000).map(|i| thread::spawn(move || f(i))).collect();

t.join();
}
``````
57
Create the list y containing the items from the list x that satisfy the predicate p. Respect the original ordering. Don't modify x in-place.
``y = list(filter(p, x))``
Alternative implementation:
``y = [element for element in x if p(element)]``
``let y: Vec<_> = x.iter().filter(p).collect();``
58
Create string lines from the content of the file with filename f.
``lines = open(f).read()``
Alternative implementation:
``````with open(f) as fo:
``````let mut file = File::open(f)?;
let mut lines = String::new();
Alternative implementation:
``let lines = fs::read_to_string(f).expect("Can't read file.");``
59
Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").
``print(x, "is negative", file=sys.stderr)``
``eprintln!("{} is negative", x);``
60
Assign to x the string value of the first command line parameter, after the program name.
``x = sys.argv``
``````let first_arg = env::args().skip(1).next();

let fallback = "".to_owned();
let x = first_arg.unwrap_or(fallback);``````
Alternative implementation:
``let x = env::args().nth(1).unwrap_or("".to_string());``
61
Assign to the variable d the current date/time value, in the most standard type.
``d = datetime.datetime.now()``
``let d = time::now();``
Alternative implementation:
``let d = SystemTime::now();``
62
Set i to the first position of string y inside string x, if exists.

Specify if i should be regarded as a character index or as a byte index.

Explain the behavior when y is not contained in x.
``i = x.find(y)``
``let i = x.find(y);``
63
Assign to x2 the value of string x with all occurrences of y replaced by z.
Assume occurrences of y are not overlapping.
``x2 = x.replace(y, z)``
``let x2 = x.replace(&y, &z);``
64
Assign to x the value 3^247
``x = 3 ** 247``
``````let a = 3.to_bigint().unwrap();
let x = num::pow(a, 247);``````
65
From the real value x in [0,1], create its percentage string representation s with one digit after decimal point. E.g. 0.15625 -> "15.6%"
``s = '{:.1%}'.format(x)``
Alternative implementation:
``s = f"{x:.01%}"``
``let s = format!("{:.1}%", 100.0 * x);``
66
Calculate the result z of x power n, where x is a big integer and n is a positive integer.
``z = x**n``
``let z = num::pow(x, n);``
67
Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers.
``````def binom(n, k):
return math.factorial(n) // math.factorial(k) // math.factorial(n - k)``````
Alternative implementation:
``````def binom(n, k):
return math.comb(n, k)``````
``````fn binom(n: u64, k: u64) -> BigInt {
let mut res = BigInt::one();
for i in 0..k {
res = (res * (n - i).to_bigint().unwrap()) /
(i + 1).to_bigint().unwrap();
}
res
}``````
68
Create an object x to store n bits (n being potentially large).
``x = bytearray(int(math.ceil(n / 8.0)))``
``let mut x = vec![false; n];``
69
Use seed s to initialize a random generator.

If s is constant, the generator output will be the same each time the program runs. If s is based on the current value of the system clock, the generator output will be different each time.
``rand = random.Random(s)``
``````let s = 32;
let mut rng = StdRng::seed_from_u64(s);``````
70
Get the current datetime and provide it as a seed to a random generator. The generator sequence will be different at each run.
``rand = random.Random()``
``````let d = SystemTime::now()
.duration_since(SystemTime::UNIX_EPOCH)
.expect("Duration since UNIX_EPOCH failed");
let mut rng = StdRng::seed_from_u64(d.as_secs());``````
71
Basic implementation of the Echo program: Print all arguments except the program name, separated by space, followed by newline.
The idiom demonstrates how to skip the first argument if necessary, concatenate arguments as strings, append newline and print it to stdout.
``print(' '.join(sys.argv[1:]))``
``println!("{}", env::args().skip(1).collect::<Vec<_>>().join(" "));``
Alternative implementation:
``println!("{}", std::env::args().skip(1).format(" "));``
73
Create a factory named fact for any sub class of Parent and taking exactly one string str as constructor parameter.
``````def fact(a_class, str_):
if issubclass(a_class, Parent):
return a_class(str_)``````
``````fn fact<Parent: std::str::FromStr>(str: String, _: Parent) -> Parent where <Parent as FromStr>::Err: Debug
{
return str.parse::<Parent>().unwrap();
}``````
74
Compute the greatest common divisor x of big integers a and b. Use an integer type able to handle huge numbers.
``x = gcd(a, b)``
Alternative implementation:
``x = math.gcd(a, b)``
``let x = a.gcd(&b);``
75
Compute the least common multiple x of big integers a and b. Use an integer type able to handle huge numbers.
``x = (a*b)//gcd(a, b)``
Alternative implementation:
``x = math.lcm(a, b)``
``let x = a.lcm(&b);``
76
Create the string s of integer x written in base 2.

E.g. 13 -> "1101"
``s = '{:b}'.format(x)``
``let s = format!("{:b}", x);``
Alternative implementation:
``let s = format!("{x:b}");``
77
Declare a complex x and initialize it with value (3i - 2). Then multiply it by i.
``````x = 3j-2
y = x * 1j``````
``````let mut x = Complex::new(-2, 3);
x *= Complex::i();``````
78
Execute a block once, then execute it again as long as boolean condition c is true.
``````while True:
do_something()
if not c:
break``````
``````loop {
doStuff();
if !c { break; }
}``````
Alternative implementation:
``````while {
doStuff();
c
} { /* EMPTY */ }``````
79
Declare the floating point number y and initialize it with the value of the integer x .
``y = float(x)``
``let y = x as f64;``
80
Declare integer y and initialize it with the value of floating point number x . Ignore non-integer digits of x .
Make sure to truncate towards zero: a negative x must yield the closest greater integer (not lesser).
``y = int(x)``
``let y = x as i32;``
81
Declare the integer y and initialize it with the rounded value of the floating point number x .
Ties (when the fractional part of x is exactly .5) must be rounded up (to positive infinity).
``y = int(x + 0.5)``
``let y = x.round() as i64;``
82
Find how many times string s contains substring t.
Specify if overlapping occurrences are counted.
``count = s.count(t)``
``let c = s.matches(t).count();``
83
Declare regular expression r matching strings "http", "htttp", "httttp", etc.
``r = re.compile(r"htt+p")``
``let r = Regex::new(r"htt+p").unwrap();``
84
Count number c of 1s in the integer i in base 2.

E.g. i=6 → c=2
``c = bin(i).count("1")``
Alternative implementation:
``c = i.bit_count()``
``let c = i.count_ones();``
85
Write boolean function addingWillOverflow which takes two integers x, y and return true if (x+y) overflows.

An overflow may be above the max positive value, or below the min negative value.
``````def adding_will_overflow(x,y):
return False``````
``````fn adding_will_overflow(x: usize, y: usize) -> bool {
}``````
86
Write the boolean function multiplyWillOverflow which takes two integers x, y and returns true if (x*y) overflows.

An overflow may reach above the max positive value, or below the min negative value.
``````def multiplyWillOverflow(x,y):
return False``````
``````fn multiply_will_overflow(x: i64, y: i64) -> bool {
x.checked_mul(y).is_none()
}``````
87
Exit immediately.
If some extra cleanup work is executed by the program runtime (not by the OS itself), describe it.
``sys.exit(1)``
``std::process::exit(0);``
88
Create a new bytes buffer buf of size 1,000,000.
``buf = bytearray(1000000)``
``let buf: Vec<u8> = Vec::with_capacity(1000000);``
89
You've detected that the integer value of argument x passed to the current function is invalid. Write the idiomatic way to abort the function execution and signal the problem.
``raise ValueError("x is invalid")``
``````enum CustomError { InvalidAnswer }

fn do_stuff(x: i32) -> Result<i32, CustomError> {
if x != 42 {
} else {
Ok(x)
}
}``````
90
Expose a read-only integer x to the outside world while being writable inside a structure or a class Foo.
``````class Foo(object):
def __init__(self):
self._x = 0

@property
def x(self):
"""
Doc for x
"""
return self._x``````
``````struct Foo {
x: usize
}

impl Foo {
pub fn new(x: usize) -> Self {
Foo { x }
}

pub fn x<'a>(&'a self) -> &'a usize {
&self.x
}

pub fn bar(&mut self) {
self.x += 1;
}
}``````
91
Read from the file data.json and write its content into the object x.
Assume the JSON data is suitable for the type of x.
``````with open("data.json", "r") as input:
``let x = ::serde_json::from_reader(File::open("data.json")?)?;``
92
Write the contents of the object x into the file data.json.
``````with open("data.json", "w") as output:
json.dump(x, output)``````
``::serde_json::to_writer(&File::create("data.json")?, &x)?``
93
Implement the procedure control which receives one parameter f, and runs f.
``````def control(f):
f()``````
``````fn control(f: impl Fn()) {
f();
}``````
94
Print the name of the type of x. Explain if it is a static type or dynamic type.

This may not make sense in all languages.
``print(type(x))``
Alternative implementation:
``print(x.__class__)``
``````fn type_of<T>(_: &T) -> &'static str {
std::intrinsics::type_name::<T>()
}

println!("{}", type_of(&x));``````
95
Assign to variable x the length (number of bytes) of the local file at path.
``x = os.path.getsize(path)``
``let x = fs::metadata(path)?.len();``
Alternative implementation:
``let x = path.metadata()?.len();``
96
Set boolean b to true if string s starts with prefix prefix, false otherwise.
``b = s.startswith(prefix)``
``let b = s.starts_with(prefix);``
97
Set boolean b to true if string s ends with string suffix, false otherwise.
``b = s.endswith(suffix)``
``let b = s.ends_with(suffix);``
98
Convert a timestamp ts (number of seconds in epoch-time) to a date with time d. E.g. 0 -> 1970-01-01 00:00:00
``d = datetime.date.fromtimestamp(ts)``
``let d = NaiveDateTime::from_timestamp(ts, 0);``
99
Assign to the string x the value of the fields (year, month, day) of the date d, in format YYYY-MM-DD.
``````d = date(2016, 9, 28)
x = d.strftime('%Y-%m-%d')``````
Alternative implementation:
``````d = date.today()
x = d.isoformat()``````
``Utc::today().format("%Y-%m-%d")``
Alternative implementation:
``````let format = format_description!("[year]-[month]-[day]");
let x = d.format(&format).expect("Failed to format the date");``````
100
Sort elements of array-like collection items, using a comparator c.
``items.sort(key=c)``
Alternative implementation:
``items.sort(key=functools.cmp_to_key(c))``
``items.sort_by(c);``
101
Make an HTTP request with method GET to the URL u, then store the body of the response in the string s.
``````with urllib.request.urlopen(u) as f:
``````
Alternative implementation:
``s = requests.get(u).content.decode()``
``````let client = Client::new();
let s = client.get(u).send().and_then(|res| res.text())?;``````
Alternative implementation:
``let s = ureq::get(u).call().into_string()?;``
Alternative implementation:
``````let mut response = reqwest::blocking::get(u)?;
let mut s = String::new();
102
Make an HTTP request with method GET to the URL u, then store the body of the response in the file result.txt. Try to save the data as it arrives if possible, without having all its content in memory at once.
``````filename, headers = urllib.request.urlretrieve(u, 'result.txt')
``````
Alternative implementation:
``````with open("results.txt", "wb") as fh:
fh.write(requests.get(u).content)``````
``````let client = Client::new();
match client.get(&u).send() {
Ok(res) => {
let file = File::create("result.txt")?;
::std::io::copy(res, file)?;
},
Err(e) => eprintln!("failed to send request: {}", e),
};``````
103
Read from the file data.xml and write its contents into the object x.
Assume the XML data is suitable for the type of x.
``x = lxml.etree.parse('data.xml')``
105
Assign to the string s the name of the currently executing program (but not its full path).
``s = sys.argv``
``````fn get_exec_name() -> Option<String> {
std::env::current_exe()
.ok()
.and_then(|pb| pb.file_name().map(|s| s.to_os_string()))
.and_then(|s| s.into_string().ok())
}

fn main() -> () {
let s = get_exec_name().unwrap();
println!("{}", s);
}``````
Alternative implementation:
``````let s = std::env::current_exe()
.expect("Can't get the exec path")
.file_name()
.expect("Can't get the exec name")
.to_string_lossy()
.into_owned();``````
106
Assign to string dir the path of the working directory.
(This is not necessarily the folder containing the executable itself)
``dir = os.getcwd()``
``let dir = env::current_dir().unwrap();``
107
Assign to string dir the path of the folder containing the currently running executable.
(This is not necessarily the working directory, though.)
``dir = os.path.dirname(os.path.abspath(__file__))``
``````let dir = std::env::current_exe()?
.canonicalize()
.expect("the current exe should exist")
.parent()
.expect("the current exe should be a file")
.to_string_lossy()
.to_owned();``````
108
Print the value of variable x, but only if x has been declared in this program.
This makes sense in some languages, not all of them. (Null values are not the point, rather the very existence of the variable.)
``````if 'x' in locals():
print(x)``````
Alternative implementation:
``````try:
x
except NameError:
print("does not exist")``````
109
Set n to the number of bytes of a variable t (of type T).
``n = pympler.asizeof.asizeof(t)``
``let n = ::std::mem::size_of::<T>();``
110
Set the boolean blank to true if the string s is empty, or null, or contains only whitespace ; false otherwise.
``blank = not s or s.isspace()``
``let blank = s.trim().is_empty();``
Alternative implementation:
``let blank = s.chars().all(|c| c.is_whitespace());``
111
From current process, run program x with command-line parameters "a", "b".
``subprocess.call(['x', 'a', 'b'])``
``````let output = Command::new("x")
.args(&["a", "b"])
.spawn()
.expect("failed to execute process");``````
Alternative implementation:
``````let output = Command::new("x")
.args(&["a", "b"])
.output()
.expect("failed to execute process");``````
Alternative implementation:
``````let output = Command::new("x")
.args(&["a", "b"])
.status()
.expect("failed to execute process");``````
112
Print each key k with its value x from an associative array mymap, in ascending order of k.
``````for k in sorted(mymap):
print(mymap[k])
``````
``````for (k, x) in mymap {
println!("({}, {})", k, x);
}``````
113
Print each key k with its value x from an associative array mymap, in ascending order of x.
Multiple entries may exist for the same value x.
``````for x, k in sorted((x, k) for k,x in mymap.items()):
print(k, x)
``````
Alternative implementation:
``````for key, value in sorted(d.items(), key=operator.itemgetter(1)):
print(key, value)``````
``````for (k, x) in mymap.iter().sorted_by_key(|x| x.1) {
println!("[{},{}]", k, x);
}``````
Alternative implementation:
``````let mut items: Vec<_> = mymap.iter().collect();
items.sort_by_key(|item| item.1);
for (k, x) in items {
println!("[{},{}]", k, x);
}``````
114
Set boolean b to true if objects x and y contain the same values, recursively comparing all referenced elements in x and y.
Tell if the code correctly handles recursive types.
``b = x == y``
``let b = x == y;``
115
Set boolean b to true if date d1 is strictly before date d2 ; false otherwise.
``b = d1 < d2``
``let b = d1 < d2;``
116
Remove all occurrences of string w from string s1, and store the result in s2.
``s2 = s1.replace(w, '')``
``s2 = s1.replace(w, "");``
Alternative implementation:
``let s2 = str::replace(s1, w, "");``
117
Set n to the number of elements of the list x.
``n = len(x)``
``````let n = x.len();

``````
118
Create the set y from the list x.
x may contain duplicates. y is unordered and has no repeated values.
``y = set(x)``
``let y: HashSet<_> = x.into_iter().collect();``
119
Remove duplicates from the list x.
Explain if the original order is preserved.
``x = list(set(x))``
Alternative implementation:
``x = list(OrderedDict(zip(x, x)))``
Alternative implementation:
``````def dedup(x):
y = []
for i in x:
if not i in y:
y.append(i)
return y``````
``````x.sort();
x.dedup();``````
Alternative implementation:
``let dedup: Vec<_> = x.iter().unique().collect();``
120
Read an integer value from the standard input into the variable n
``n = int(input("Input Prompting String: "))``
``````fn get_input() -> String {
let mut buffer = String::new();
buffer
}

let n = get_input().trim().parse::<i64>().unwrap();``````
Alternative implementation:
``````let mut input = String::new();
let n: i32 = input.trim().parse().unwrap();``````
Alternative implementation:
``````let n: i32 = std::io::stdin()
.lock()
.lines()
.next()
.expect("stdin should be available")
.trim()
.parse()
.expect("input was not an integer");``````
Alternative implementation:
``````let n: i32 = read!();
``````
121
Listen UDP traffic on port p and read 1024 bytes into buffer b.
``````sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind((UDP_IP, p))
while True:
``````let mut b = [0 as u8; 1024];
let sock = UdpSocket::bind(("localhost", p)).unwrap();
sock.recv_from(&mut b).unwrap();``````
122
Create an enumerated type Suit with 4 possible values SPADES, HEARTS, DIAMONDS, CLUBS.
``````class Suit:
SPADES, HEARTS, DIAMONDS, CLUBS = range(4)``````
Alternative implementation:
``````class Suit(Enum):
HEARTS = 2
DIAMONDS = 3
CLUBS = 4``````
``````enum Suit {
Hearts,
Diamonds,
Clubs,
}``````
123
Verify that predicate isConsistent returns true, otherwise report assertion violation.
Explain if the assertion is executed even in production environment or not.
``assert isConsistent``
``assert!(is_consistent);``
124
Write the function binarySearch which returns the index of an element having the value x in the sorted array a, or -1 if no such element exists.
``````def binarySearch(a, x):
i = bisect.bisect_left(a, x)
return i if i != len(a) and a[i] == x else -1
``````
``a.binary_search(&x).unwrap_or(-1);``
125
measure the duration t, in nanoseconds, of a call to the function foo. Print this duration.
``````t1 = time.perf_counter_ns()
foo()
t2 = time.perf_counter_ns()
print('Nanoseconds:', t2 - t1)``````
``````let start = Instant::now();
foo();
let duration = start.elapsed();
println!("{}", duration);
``````
126
Write a function foo that returns a string and a boolean value.
``````def foo():
return 'string', True
``````
``````fn foo() -> (String, bool) {
(String::from("bar"), true)
}``````
127
Import the source code for the function foo body from a file "foobody.txt".
``foo = imp.load_module('foobody', 'foobody.txt').foo``
``````fn main() {
include!("foobody.txt");
}
``````
128
Call a function f on every node of a tree, in breadth-first prefix order
``````def BFS(f, root):
Q = [root]
while Q:
n = Q.pop(0)
f(n)
for child in n:
if not n.discovered:
n.discovered = True
Q.append(n)``````
``````struct Tree<V> {
children: Vec<Tree<V>>,
value: V
}

impl<V> Tree<V> {
fn bfs(&self, f: impl Fn(&V)) {
let mut q = VecDeque::new();
q.push_back(self);

while let Some(t) = q.pop_front() {
(f)(&t.value);
for child in &t.children {
q.push_back(child);
}
}
}
}``````
129
Call the function f on every vertex accessible from the vertex start, in breadth-first prefix order
``````def breadth_first(start, f):
seen = set()
q = deque([start])
while q:
vertex = q.popleft()
f(vertex)
q.extend(v for v in vertex.adjacent if v not in seen)``````
``````struct Vertex<V> {
value: V,
neighbours: Vec<Weak<RefCell<Vertex<V>>>>,
}

// ...

fn bft(start: Rc<RefCell<Vertex<V>>>, f: impl Fn(&V)) {
let mut q = vec![start];
let mut i = 0;
while i < q.len() {
let v = Rc::clone(&q[i]);
i += 1;
(f)(&v.borrow().value);
for n in &v.borrow().neighbours {
if q.iter().all(|v| v.as_ptr() != n.as_ptr()) {
q.push(n);
}
}
}
}``````
130
Call th function f on every vertex accessible from the vertex v, in depth-first prefix order
``````def depth_first(start, f):
seen = set()
stack = [start]
while stack:
vertex = stack.pop()
f(vertex)
stack.extend(
v for v in vertex.adjacent if v not in seen
)``````
``````struct Vertex<V> {
value: V,
neighbours: Vec<Weak<RefCell<Vertex<V>>>>,
}

// ...

fn dft_helper(start: Rc<RefCell<Vertex<V>>>, f: &impl Fn(&V), s: &mut Vec<*const Vertex<V>>) {
s.push(start.as_ptr());
(f)(&start.borrow().value);
for n in &start.borrow().neighbours {
if s.iter().all(|&p| p != n.as_ptr()) {
Self::dft_helper(n, f, s);
}
}
}``````
131
Execute f1 if condition c1 is true, or else f2 if condition c2 is true, or else f3 if condition c3 is true.
Don't evaluate a condition when a previous condition was true.
``f1() if c1 else f2() if c2 else f3() if c3 else None``
Alternative implementation:
``````if c1:
f1()
elif c2:
f2()
elif c3:
f3()``````
``if c1 { f1() } else if c2 { f2() } else if c3 { f3() }``
Alternative implementation:
``````match true {
_ if c1 => f1(),
_ if c2 => f2(),
_ if c3 => f3(),
_ => (),
}``````
132
Run the procedure f, and return the duration of the execution of f.
``duration = timeit.timeit("f()", setup="from __main__ import f")``
Alternative implementation:
``````start = time.time()
f()
end = time.time()
return end - start``````
``````let start = Instant::now();
f();
let duration = start.elapsed();``````
133
Set boolean ok to true if string word is contained in string s as a substring, even if the case doesn't match, or to false otherwise.
``ok = word.lower() in s.lower()``
``````let re = Regex::new(&format!("(?i){}", regex::escape(word))).unwrap();
let ok = re.is_match(&s);``````
Alternative implementation:
``````let re =
RegexBuilder::new(&regex::escape(word))
.case_insensitive(true)
.build().unwrap();

let ok = re.is_match(s);``````
Alternative implementation:
``let ok = s.to_ascii_lowercase().contains(&word.to_ascii_lowercase());``
134
Declare and initialize a new list items, containing 3 elements a, b, c.
``items = [a, b, c]``
``let items = vec![a, b, c];``
135
Remove at most 1 item from list items, having the value x.
This will alter the original list or return a new list, depending on which is more idiomatic.
If there are several occurrences of x in items, remove only one of them. If x is absent, keep items unchanged.
``items.remove(x)``
``````if let Some(i) = items.first(&x) {
items.remove(i);
}``````
136
Remove all occurrences of the value x from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
``newlist = [item for item in items if item != x]``
``items = items.into_iter().filter(|&item| item != x).collect();``
Alternative implementation:
``items.retain(|&item| item != x);``
137
Set the boolean b to true if the string s contains only characters in the range '0'..'9', false otherwise.
``````b = s.isdigit()
``````
``````let chars_are_numeric: Vec<bool> = s.chars()
.map(|c|c.is_numeric())
.collect();
let b = !chars_are_numeric.contains(&false);``````
Alternative implementation:
``let b = s.chars().all(char::is_numeric);``
Alternative implementation:
``let b = s.bytes().all(|c| c.is_ascii_digit());``
138
Create a new temporary file on the filesystem.
``file = tempfile.TemporaryFile()``
``````let temp_dir = TempDir::new("prefix")?;
let temp_file = File::open(temp_dir.path().join("file_name"))?;``````
139
Create a new temporary folder on filesystem, for writing.
``td = tempfile.TemporaryDirectory()``
``let tmp = TempDir::new("prefix")?;``
140
Delete from map m the entry having key k.

Explain what happens if k is not an existing key in m.
``m.pop(k, None)``
``m.remove(&k);``
141
Iterate in sequence over the elements of the list items1 then items2. For each iteration print the element.
``````for x in items1 + items2:
print(x)
``````
``````for i in item1.iter().chain(item2.iter()) {
print!("{} ", i);
}``````
142
Assign to string s the hexadecimal representation (base 16) of integer x.

E.g. 999 -> "3e7"
``s = hex(x)``
``let s = format!("{:X}", x);``
143
Iterate alternatively over the elements of the lists items1 and items2. For each iteration, print the element.

Explain what happens if items1 and items2 have different size.
``for pair in zip(item1, item2): print(pair)``
``````for pair in izip!(&items1, &items2) {
println!("{}", pair.0);
println!("{}", pair.1);
}``````
144
Set boolean b to true if file at path fp exists on filesystem; false otherwise.

Beware that you should never do this and then in the next instruction assume the result is still valid, this is a race condition on any multitasking OS.
``b = os.path.exists(fp)``
Alternative implementation:
``b = Path(fp).exists()``
``````let b = std::path::Path::new(fp).exists();
``````
145
Print message msg, prepended by current date and time.

Explain what behavior is idiomatic: to stdout or stderr, and what the date format is.
``````logging.basicConfig(stream=sys.stdout, level=logging.DEBUG, format="%(asctime)-15s %(message)s")
logger = logging.getLogger('NAME OF LOGGER')

logger.info(msg)``````
``eprintln!("[{}] {}", humantime::format_rfc3339_seconds(std::time::SystemTime::now()), msg);``
146
Extract floating point value f from its string representation s
``````s = u'545,2222'
locale.setlocale(locale.LC_ALL, 'de')
f = locale.atof(s)``````
Alternative implementation:
``f = float(s)``
Alternative implementation:
``f = float(s)``
``let f = s.parse::<f32>().unwrap();``
Alternative implementation:
``let f: f32 = s.parse().unwrap();``
147
Create string t from string s, keeping only ASCII characters
``t = re.sub('[^\u0000-\u007f]', '',  s)``
Alternative implementation:
``t = s.encode("ascii", "ignore").decode()``
``let t = s.replace(|c: char| !c.is_ascii(), "");``
Alternative implementation:
``let t = s.chars().filter(|c| c.is_ascii()).collect::<String>();``
148
Read a list of integer numbers from the standard input, until EOF.
``list(map(int, input().split()))``
Alternative implementation:
``numbers = [int(x) for x in input().split()]``
``````let mut string = String::new();
let result = string
.lines()
.map(i32::from_str)
.collect::<Result<Vec<_>, _>>();``````
150
Remove the last character from the string p, if this character is a forward slash /
``p = p.rstrip("/")``
``if p.ends_with('/') { p.pop(); }``
151
Remove last character from string p, if this character is the file path separator of current platform.

Note that this also transforms unix root path "/" into the empty string!
``````if p.endswith(os.sep):
p = p[:-1]``````
``````let p = if ::std::path::is_separator(p.chars().last().unwrap()) {
&p[0..p.len()-1]
} else {
p
};``````
Alternative implementation:
``p = p.strip_suffix(std::path::is_separator).unwrap_or(p);``
152
Create string s containing only the character c.
``s = c``
``let s = c.to_string();``
153
Create the string t as the concatenation of the string s and the integer i.
``t = '{}{}'.format(s,i)``
Alternative implementation:
``t = f'{s}{i}'``
``````let t = format!("{}{}", s, i);
// or
let t = format!("{s}{i}");``````
154
Find color c, the average between colors c1, c2.

c, c1, c2 are strings of hex color codes: 7 chars, beginning with a number sign # .
Assume linear computations, ignore gamma corrections.
``````r1, g1, b1 = [int(c1[p:p+2], 16) for p in range(1,6,2)]
r2, g2, b2 = [int(c2[p:p+2], 16) for p in range(1,6,2)]
c = '#{:02x}{:02x}{:02x}'.format((r1+r2) // 2, (g1+g2) //2, (b1+b2)// 2)``````
Alternative implementation:
``````class RGB(numpy.ndarray):
@classmethod
def from_str(cls, rgbstr):
return numpy.array([
int(rgbstr[i:i+2], 16)
for i in range(1, len(rgbstr), 2)
]).view(cls)

def __str__(self):
self = self.astype(numpy.uint8)
return '#' + ''.join(format(n, 'x') for n in self)

c1 = RGB.from_str('#a1b1c1')
print(c1)
c2 = RGB.from_str('#1A1B1C')
print(c2)

print((c1 + c2) / 2)``````
``"Too long for text box, see online demo"``
155
Delete from filesystem the file having path filepath.
``````path = pathlib.Path(_filepath)
Alternative implementation:
``os.remove(filepath)``
``let r = fs::remove_file(filepath);``
156
Assign to the string s the value of the integer i in 3 decimal digits. Pad with zeros if i < 100. Keep all digits if i1000.
``s = format(i, '03d')``
``let s = format!("{:03}", i);``
157
Initialize a constant planet with string value "Earth".
``PLANET = 'Earth'``
``const PLANET: &str = "Earth";``
158
Create a new list y from randomly picking exactly k elements from list x.

It is assumed that x has at least k elements.
Each element must have same probability to be picked.
Each element from x must be picked at most once.
Explain if the original ordering is preserved or not.
``y = random.sample(x, k)``
``````let mut rng = &mut rand::thread_rng();
let y = x.choose_multiple(&mut rng, k).cloned().collect::<Vec<_>>();``````
159
Define a Trie data structure, where entries have an associated value.
(Not all nodes are entries)
``````class Trie:
def __init__(self, prefix, value=None):
self.prefix = prefix
self.children = []
self.value = value``````
``````struct Trie {
val: String,
nodes: Vec<Trie>
}``````
160
Execute f32() if platform is 32-bit, or f64() if platform is 64-bit.
This can be either a compile-time condition (depending on target) or a runtime detection.
``````if sys.maxsize > 2**32:
f64()
else:
f32()

``````
``````match std::mem::size_of::<&char>() {
4 => f32(),
8 => f64(),
_ => {}
}``````
Alternative implementation:
``````#[cfg(target_pointer_width = "64")]
f64();

#[cfg(target_pointer_width = "32")]
f32();	``````
161
Multiply all the elements of the list elements by a constant c
``elements = [c * x for x in elements]``
``let elements = elements.into_iter().map(|x| c * x).collect::<Vec<_>>();``
Alternative implementation:
``elements.iter_mut().for_each(|x| *x *= c);``
162
execute bat if b is a program option and fox if f is a program option.
``````if 'b' in sys.argv[1:]: bat()
if 'f' in sys.argv[1:]: fox()
``````
Alternative implementation:
``````options = {
'b': bat
'f': fox
}

for option, function in options:
if option in sys.argv[1:]:
function()``````
``````if let Some(arg) = ::std::env::args().nth(1) {
if &arg == "f" {
fox();
} else if &arg = "b" {
bat();
} else {
eprintln!("invalid argument: {}", arg),
}
} else {
eprintln!("missing argument");
}``````
Alternative implementation:
``````if let Some(arg) = ::std::env::args().nth(1) {
match arg.as_str() {
"f" => fox(),
"b" => box(),
_ => eprintln!("invalid argument: {}", arg),
};
} else {
eprintln!("missing argument");
}``````
163
Print all the list elements, two by two, assuming list length is even.
``````for x in zip(list[::2], list[1::2]):
print(x)``````
Alternative implementation:
``````def pairwise(iterable):
"s -> (s0,s1), (s1,s2), (s2, s3), ..."
a, b = tee(iterable)
next(b, None)
return zip(a, b)

for a, b in pairwise(list):
print(a, b)``````
``````for pair in list.chunks(2) {
println!("({}, {})", pair, pair);
}``````
164
Open the URL s in the default browser.
Set the boolean b to indicate whether the operation was successful.
``webbrowser.open(s)``
``````webbrowser::open(s).expect("failed to open URL");
``````
165
Assign to the variable x the last element of the list items.
``x = items[-1]``
``let x = items[items.len()-1];``
Alternative implementation:
``let x = items.last().unwrap();``
166
Create the list ab containing all the elements of the list a, followed by all the elements of the list b.
``ab = a + b``