Python, as of version 3.6, includes two different random modules.
The module called random is pseudo-random, meaning it does not generate
true randomness, but follows an algorithm that simulates randomness.
Since random numbers are generated through a known algorithm, they are not truly random.
The random module is not correctly suited for cryptography and should not be used,
precisely because it is pseudo-random.
For this reason, in version 3.6, Python introduced the secrets module, which generates
cryptographically strong random numbers that provide the greater security required for cryptography.
Since this is only an exercise, random is fine to use, but note that it would be
very insecure if actually used for cryptography.