Copy Arrays and Lists

This is how you copy an Array / a List correctly.

Let’s create an Array / List first:

a = ["Simon", "Laura"]

Then copy it properly!

in Python

b = a[:]

in Ruby

b = a.map(&:clone)

The following example shows the “false friend declaration”

By simply declaring the array variable a to a new variable b, then b points to a. So every change of a means change in b and vice versa.

Now add a new value to a:

Python

a = ["Simon", "Laura"]
b = a
a.append("Willi")
print(b)

Ruby

a = ["Simon", "Laura"]
b = a
a.push("Willi")
put b

In both cases b will return ["Simon", "Laura", "Willi"]