Check validity of username at signup

[martinzlocha]

Detailed Description

When a student is signing up the form should check whether the provided username is valid.

Context

This change will reduce the number of usernames submitted which contain typo's. It will also verify that the username provided isn't an arbitrary string.

Possible Implementation

Validating of user input into forms is done within forms.py. Usage of RegEx is preferred over manual string parsing. If an invalid username is provided then the form should raise a ValidationError.

Example of valid usernames:

• mz4315
• abc13
• xy12315
• ab117

Example of invalid usernames:

• a1216
• abcf16
• a1b17
• ab1210

[plietar]

Why is ab1210 a bad username ?

In general I don't see a point in checking usernames against a pattern. You'll need to check them against the real database eventually

[martinzlocha]

I considered it bad because the student arrived to Imperial in 2010 therefore isnt a UG student probably.

The issue is that TeachDB is updated very late (late September) and I'm not sure when are other databases updated and if we have access to them. Given that we want to allocate the students ASAP it will be too late.

[jamesprinc3]

I considered it bad because the student arrived to Imperial in 2010 therefore isnt a UG student probably.

I don't think we should be inferring this much at a regex stage. Probably better to just check that there are some numbers and there are some letters, and they are below some sensible limit.

[levex]

Possible regexp candidate: ^[A-z]{2,3}\d+$

[martinzlocha]

Even better ^([A-z]{2}\d{3,5}|[A-z]{3}\d{2})$ if you want to be more specific.

Edit: This won't actually work for everyone, use ^[A-z]{2,3}\d{2,5}$ instead.