Combine a simple value with a list

Question

[What's the idiomatic syntax for prepending to a short python list? is about modifying an existing list, and doesn't contain a suitable answer to this question. While a solution can be found in one its answers, it's not the best one.]

Is there a simple way to combine simple values and/or the elements of a list into a flat list?

For example, given

lst = [ 5, 6, 7 ]
x = 4

Is there a simple way to produce

result = [ 4, 5, 6, 7 ]

The following is satisfactory, but I'm sure there's a cleaner way to do this:

result = [ x ]
result.extend(lst)

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Perl:

my @array = ( 5, 6, 7 );
my $x = 4;
my @result = ( $x, @array );

JavaScript (ES6):

let array = [ 5, 6, 7 ];
let x = 4;
let result = [ x, ...list ];

Answer 1

You can concatenate two lists (or two tuples).

result = [x] + lst

You could use the iterable unpacking operator on arbitrary iterables.

result = [x, *lst]

If you have a iterable you only want to make look flat rather than actually flattened, you can use itertools.chain to create an iterable generator.

import itertools
result = itertools.chain([x], lst)

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If you're ok with prepending to the existing list instead of creating a new one, solution can be found here.

Answer 2

There is indeed, you have the + operator to concatenate lists

[x] + [ 5, 6, 7 ]
# [4, 5, 6, 7]

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You could also use the iterable unpacking operator:

l = [ 5, 6, 7 ]

[x, *l]
[4, 5, 6, 7]

---

Or you can also use list.insert:

l.insert(0, x) 

print(l)
[4, 5, 6, 7]