Allow custom challenge order

[piglei]

Currently the challenges appear in alphabetical order, it would be better if we customize the order by prioritizing the easier challenges to the top. For example, the basic challenges could use this order:

# The basic syntax
- parameter
- return
- variable
- any
- kwargs
# Composite data types
- list
- dict
- tuple
# Other
- typealias
- union
- optional
- final

This would make the experience better as people go through the challenges from top to bottom.

[laike9m]

Agree this can be improved, but not at the cost of extra complexity. It seems that to change the order, we would always need to store it somewhere else, which is a no-go to me.

[piglei]

Agree this can be improved, but not at the cost of extra complexity. It seems that to change the order, we would always need to store it somewhere else, which is a no-go to me.

Yes, the order has to be stored somewhere, at least we might need to use flask's project `Config' object. One approach might be this:

• Introduce a project config variable: challenge_order: List[challenge name].
• When getting challenges, use the above list as an index.
• If the challenge is missing from the index, put it to the bottom and use alphabetical order.
• This means that if challenge_order is empty, the system would work normally as well.

[laike9m]

Thanks for proposing the solution. Though it may change in the future, at this point, I don't think this is something worth adding.

[piglei]

OK. I would love to contribute if you change your mind in the future. 😁