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chcko randomly parameterized exercises automatically checked (formerly mamchecker)

Project description


Educational problem server at

developed at

with example content package

ch[e]cko.e[d]u wants to collect science problems, usable by students with or without learn coaches around the world, as an infrastructure.

The content packages are python packages.


  • Collect problems
  • Make the problems readily usable, also over the distance
  • Make it less effort
    • to check one’s own understanding
    • to check the progress of students
    • to compose a school or home work
    • to correct (as the server takes care of that)

Help Bootstrap the Community

chcko can be installed locally, too. But allows you to do without own hardware and server maintenance

Currently is only on gcloud free quota, which is regularly used up.

Running for a broader community produces less overall cost, though, than everyone having their own servers.

If you can identify with the goals of this project, help bootstrap the community,

  • first by a small donation to raise the server quota
  • and second by contributing your own problem packages (example: chcko-r)

Not just teacher, also students can make a chcko-X package out of problems they solve. Since they solve the problems anyway,

  • why not using Python?
  • and why not sharing the problems?


Pages are requested with this URL format:


Pages are:

  • org: add roles and choose a role color
  • contents: specific content items or overview if no query
  • done: done problems
  • todo: assigned problems
  • some additional helper pages

Example URLs:

With && instead of one & as separator in a contents query (course), only one problem at a time is shown. &&& marks the current position. For example, .../en/contents? has r.a as current item in the course.

The names School, Field, Teacher, Class, Role form namespace levels to describe a student role. The namespaces are of organizational nature. The namepace names are taken from usual organizational structures. What string is used in each level is up to the user.

See also queries.

Use Cases

No Login

Without login a random Role is generated. One can revisit the Role later via the URL, for example

With Org one can choose names. One can choose names via the URL, too. For example:

Without login these names, random or not, are not protected. Their ownership changes to a logged-in user when accessed, either via Org or via URL.

Step-by-step try in class without logging in:

Reserve a Name

Login in.


Create a Class

In the Org tab, the Role input box uses the first of ;, as a separator to create a whole class with no owner (independent of logged in or not).

Then send a link to each student (e.g. via email):

Or send the same link to all students and let them add their StudentName.

If the students log in, before visiting the URL, they take ownership of the role.


To assign to others, you need to be logged in.

In the contents tab choose the problems or use an URL:

At the end of the page you can choose classes or students to assign to. Assigning a course (with the && instead of &), assigns the problems individually.

URLs without problems cannot be assigned.

The students

  • log in
  • go to the Todo tab
  • solve the assigned problems

Find problems

There is no full text search engine yet. To find a problem, there are these alternatives:

Create Printout

If you add bare to the query string of the problem URL, header and footer is dropped. There is a printer symbol at the bottom right, which does that. Then you can

  • save and open the file with a MS Word or Libre Office
  • print from within your browser (possibly to a pdf file)
  • use the command line with chrome or chromium to create a PDF
chrome --enable-logging --headless --disable-gpu --print-to-pdf=/full/path/to.pdf

Check Done

You can check the done problems below a namespace level like class

  • if you own the level and you are logged in
  • if the level is not owned

Change to the teacher / class / Role.

Clicking on the names for class, teacher, … forwards to these URLs.

* can be replaced by %2A when sending the link, because some programs drop the *.

?<school>&<field>&<teacher>&<class>&<role>&<problem> is defaulted to the left with the current role names if omitted. *&* means: don’t take the default, but show any role and problem.

See also done.

Remove an Assignment

The todo page has the same query format as the done page.*&*

Shows the given (and not yet done) assignments and allows to delete them selectively.

Assume Role

As a logged in user you can have more roles. These roles are listed by clicking in the role field around the ☰. Click on an entry to assume another role.

Remove a Role

  • Assume the role
  • Go to the Org tab
  • Choose delete
  • Confirm

There should be no easier way, because you lose all the history of the role, by deleting it.

Change a Role

Same as Remove a Role, but choose change instead.

This moves all the history associated with a role to the new role and deletes the previous one.

change is a way to

  • leave a class (teacher, field, school) and
  • join another class

without loosing one’s history.

Content Packages

In a content package

  • content items <package_id>.<content_id> of the URL query
  • correspond to the folder chcko-<package_id>/chcko/<package_id>/<content_id>/

Example content package layout:

  ├── chcko
  │   ├──
  │   ├── _images
  │   │   ├── r_dg_c1.png
  │   │   ├── ...
  │   └── r
  │       ├──
  │       ├──
  │       ├── a
  │       │   ├── de.html
  │       │   ├── en.html
  │       │   └──
  │       ├── b
  │       │   ├── _de.html
  │       │   ├── de.rst
  │       │   ├── _en.html
  │       │   ├── en.rst
  │       │   ├──
  │       │   └── vector_dot_cross.tex
  │       └── ...
  ├── ...
  ├── README.rst

Image file names in _images are either random or otherwise unique by encoding package ID, problem ID, content and possibly language. is always there. Altogether it is a Python package, with chcko namespace

Generated files start with _ (_<language_id>.html). <language_id>.rst can contain tikz images. <language_id>.rst files are statically converted to _<language_id>.html with:

doit -kd. html fills the database with content items. It is generated using:

doit -kd. initdb

Often it is better to just stick to HTML, though. HTML files are actually stpl template snippets, for example r/a/en.html:

%path = "maths/trigonometry/sss"
%kind = 0 #problems (``chindnum`` converts from current's language kind names, see
%level = 11 # school year starting from elementary
The sides of a triangle are
a={{ chiven.a }},
b={{ chiven.b }},
c={{ chiven.c }}.
How big are the angles (in degrees).
%champles=['e.g.'+e for e in ['23.3','100','56.7']]

Every content item must have the first 3 lines starting with %path, %kind and %level. They are used by doit -kd. initdb to create the index.

The global defines for problem templates are made distinguishable from english words by replacing the first consonant with ch.

chiven is what chiven() in returns.

chq (defined in chelper.html ) creates the input field or shows the result, according the output of chalc() (normally a list of numbers), if no idx is specified.

chq uses

  • chesults: calcuated result (from chalc())
  • chanswers: answer given by user
  • chanswered: None or datetime, when answered
  • choints: points for the answer
  • choks: answers that are OK (entries convertible to bool)

chq optionally uses (if defined):

  • chames: as input names (per idx a html/tex string, e.g. r”(alpha)”)
  • champles: input examples ( ” )
  • chadios: texts for radio buttons (a tuple per idx). chalc() returns index number.
  • checkos: texts for check boxes (a tuble per idx). chalc() returns list of indices as string of capital letters e.g. AC (chr(65+i)).
  • chow: function that shows the result, e.g. util.tx

If chq() is called for one idx only, the wrapping in a list can be dropped.

Here is the of the example:

import random
import math as m
from chcko.chcko.hlp import Struct
def angle_deg(i, g):
    d = dict(zip('abc', ([chiven.a, chiven.b, chiven.c]*2)[i:]))
    return eval('180*acos((a*a+b*b-c*c)/2/a/b)/pi', {**d,'acos':m.acos,'pi':m.pi})
def chiven():
    a, b = random.sample(range(1, 10), 2)
    c = random.randrange(max(a - b + 1, b - a + 1), a + b)
    return Struct(a=a, b=b, c=c)
def chalc(g):
    return [angle_deg(i, g) for i in range(3)]
names = [r'\(\alpha=\)', r'\(\beta=\)', r'\(\gamma=\)'] provides:

  • chiven(): returns Struct of given, randomly generated numbers
  • chalc(): returns a list of wanted results as strings (number string for chadios, strings of A-Z for OK checkos)
  • chorm(): optional function chorm() to normalize the answer to make it comparable to the result
  • chequal(): optional function to compare each index of chanswers and chesults

All other special defines of a problem in are also made available to the template.

The entries in the dict (Struct) returned from chiven() can be overridden via the URL parameters.

cheader URL parameter is text placed at the beginning of a page with problems.

A problem can also define its own javascript. As an example: r.i does %include('r/i/coord'), which has a js script per problem number chumber (see the result: r.i).

%def script():
    <script type="text/javascript" src="/static/graph.js">

%def script():
    <script type="text/javascript">
    %for i,f in enumerate(chiven.funcs):
      function fun{{chumber}}{{i}}(x) { {{f[1]}}; }
    function drawall{{chumber}}() {
        var cs = createCS("{{chumber}}","cs_div{{chumber}}");
        cs.context.font = "20px sans-serif";
        % for i,f in enumerate(chiven.funcs):
            lastpos ={{chumber}}{{i}},{{i}},2);

Non-problem texts are OK, too, but should be context-free, as they are combined with other texts/problems to a page via an URL query string.

Create a Content Package

Look at the example content package for guidance

To add a new content package on will be updated timely.

You can also run a server locally with:


If chcko is not installed:

./ -s wsgiref
#prepend ``python3`` if your default python is python2

Not installed content packages must be parallel to the main chcko folder.

With installed chcko:

pip install --user chcko
#use pip3 if your default python is python2

Create a new content package with:

runchcko --init chcko-<id>

You run this command also to fill a repo you started on github and cloned local.

Add a new content item with:

doit -kd. new


doit -kd. newrst

Edit the problem text in en.html using a text editor. See the example above.

Then, from the root of the content package:

doit -kd. html
doit -kd. initdb


make html

To test, run the server with:

runchcko [-s wsgiref]


If you are familiar with Linux, use it, possibly on a virtual machine like virtualbox. But all the needed tools are also available for Windows and MacOS.

You will need

On MacOS the developer command line tools are offered for install, when you type git in the terminal. Python3 will also be available, then.

To install the python packages for development, in a terminal in a folder of your choice:

git clone
cd chcko
pip install --user -r requirements_dev.txt
#use pip3 if your default python is python2 (e.g. MacOS)
cd ..
git clone

Sphinx is only needed if you use RST. Latex is needed, if you use Sphinx plugins (sphinxcontrib.tikz, sphinxcontrib.texfigure).

Content packages can have their own python dependencies. Installing them, makes sure these are there. Otherwise an install is not needed, if the content packages are parallel to chcko.

To run the server without installing:

cd chcko
./ -s wsgiref
#prepend ``python3`` if your default python is python2

To install:

pip install --user chcko
pip install --user chcko-r
#use pip3 if your default python is python2

To run the server with installed packages:



There are some other defines for the templates:

  • chelf: the class for the page (see folders in main chcko packages)
  • chutil: instance of Util defined in chcko/
  • chlangs: list of all languages figuring in any of the content packages
  • chdb: database class defined in chcko/ or chcko/ with mixin from chcko/
  • chuery: the current query string
  • chlang: current language (<domain>/<chlang>[/<page>]?<query>)
  • chindnum(), chumkind(): convert between kind number and string for current language (e.g. "Problem" <-> 0, see

Now some historical development background.


Chcko is yet another solution for computer aided instructions (CAI). The internet has a huge potential in teaching and learning.

The main purpose:

  • Automatically correct problems
  • Infrastructure to organize teaching (school, field, teacher, class, role/student)
  • allow teachers/coaches to quickly check the problems of students
  • The use is of course not confined to schools. Teachers, professors, tutors, coaches, students, autodidacts, … can add problems and check themselves or others.
  • Share content via separate content packages, like chcko-r.
  • The numbers in problems are randomly generated. This way a problem can be reused. Students sitting next to each others in class will have different numbers and therefore cannot copy the results.

Chcko can be used remotely as well as in class.

In class students can use the browser on their smartphones to answer problems. Teachers can immediately see, who answered correctly or who has not yet answered. This way the teacher is faster to find those students who have not yet memorized something or have not yet understood a concept or a relationship.

Students can do problems immediately after the teacher’s explanation in class in the same lesson. This way the students

  • need to pay attention, because they will have to know immediately afterwards
  • cannot copy from others, because the numbers are different, even with problems only due in the next lesson
  • do not need to admit that they have not understood, because the teacher sees, if they are unable to do the problem. Some students are too shy to ask. There are other reasons, why student’s incomprehension can stay unnoticed for too long.

The teacher cannot look at all the done problems of a class at the same time, but the software can. To do it sequentially in class would hold up the students. If the teacher takes the exercise books home, there is an unwanted delay in feedback for the students.

More parallelism in class is very important in order to make the time spent there worthwhile for the students.

The time spent by a teacher to correct exercise books is also better invested in a good preparation:

  • how to motivate the students
  • how to present the topic as easy as possible
  • which questions to ask to practice and to verify that the students have understood


  • Every content has a unique ID = ID_author.ID_content. This way no ID coordination is necessary once the author has an ID. ID_author is the same as package_id in chcko-<package_id>.

  • Every ID is also a folder

    • ID_author
      • ID_content1
      • ID_content2
  • IDs shall be as short as possible. They are best numbered through using a-z

    • numbers would not make it a Python identifier
    • capital letters would collide with windows case insensitivity for file names
  • Every content folder contains Python code and language files

    • A Python part ( to randomly generate for problems. It is also needed for content without numbers: just keep it empty.
    • Language template files (en.html, de.html, it.html, fr.html,…) that will produce html. en.html should always be there as starting points for translations.
    • A static off-line step is possible. This allows to create content from other formats, currently from restructured text files (.rst) using Sphinx. This allows to use Sphinx contributions like tikz and texfigure (tex, tikz, chemfig, …) to create graphics.
  • Human language context paths to problems are language dependent and are therefore in the language files.

  • More problems can be combined in one URL / http request (contents query) e.g. to make a larger assignment.

  • Problem/Content pages can reference other content or inline it via the template engine (% include(``) for html or or :inl:`` for RST).

  • Answers to problems are stored in a DB and combined with the language texts during loading.

  • A role is identified by an ID path/hierarchy:

    school 1-n field 1-n teacher 1-n class 1-n role
  • Via this hierarchy a teacher has fast access to the done problems of his classes and students via an URL query.

  • Teachers can assign problems to their classes/students, which they access via a todo query

  • Teachers see what their classes/students have done so far (done query)

  • Users initially get a generated role (generated random strings for each), which they can change, though (org query). There users can choose a color to help then see in which role they are.

  • Registered users can have more roles. Registration can also be done via Google, Twitter, Facebook or LinkedIn.


The code tries to stay minimal: Python 3 with bottle and a DB for the roles and problems.


The data model is:

school 1-n field 1-n teacher 1-n class 1-n role 1-n problem

The first 5 are called a role. A user has more roles.

DB is there for answers to problems, not for the problem texts.

  • On GCP, the DB is DataStore using ndb
  • On other server the DB is a SQL database using SqlAlchemy

Environment Variables

CHCKOSECRET:a secret used to encode the user token cookie
CHCKOPORT:used to change port for local server
 for social login
 for social login


The URL format is:

URL = "https://"domain"/"lang"/"page"
domain = ""
lang = "en"|"de"|...
page = ["contents"]["?"{author"."problem["="count]"&"}]
       | "done"[rlinc]
       | "todo"
       | "org"
rlinc = [[[[[school&]field&]teacher&]class&]role&]("*"|query)
query = {field("~"|"="|"!"|"<"|">")value","}

If <lang> is dropped, the last language or the browser setting is used. See

<page> is one of contents, done, todo, org. contents is default, if dropped.

<query> starts after the ?. <query> is a &-separated list. <query> can contain School=<...>&Field=<...>&Teacher=<...>&Class=<...>&Role=<...> for all pages.


With ../<lang>/contents all current contents are listed. One can select more entries here.

../en/contents?r.a& (r.a is equivalent to r.a=1) would create an English content page with one r.a and two problems. ../en/?r.a& is the same, i.e. contents is the default page.

Use && instead of & to show one problem at a time (course).

For logged-in users it is possible to make assignments to class/students with the same School-Field-Teacher prefix. You must have created the teacher role, before the others.

Problems have more questions and every question has points associated (default 1). After checking the entered values at the top there will be a summary of achieved points/total points twice, once not counting fields left empty.

The contents index can be limited with:

  • link: the author id
  • level: corresponds to school year starting from elemntary (1, 2, …)
  • kind: problems texts courses examples summaries formal fragments remarks citations definitions theorems corollaries lemmas propositions axioms conjectures claims identities paradoxes meta
  • path: as given in the header of the content sources


../<lang>/done lists the done problems with date and time and whether they were correct. One can open every done problem or do it again. It is possible to delete the selected problems.

The query



  • a student to filter his problems
  • a teacher to see the problems of his classes or students

Omitted entries on the left will be filled by the corresponding current role IDs. Therefore a student only needs <problem>, if it should be filtered at all. <..> are placeholders for the actual strings.

For ‘no restriction’ * is used.

An entry has this format:

name|field op value[,field op value[,...]]
  • name is the name of the record

  • field is a field of the record

    All records have a name, userkey and chreated. School, Field, Teacher and Class have no other fields. In addition Role has color and Problem has chuery, chlang, chiven, chreated, chanswered, chinputids, chesults, choks, choints, chanswers, chumber.

  • op consists of ~=!<>, where ~ means =. For the age of a problem (since chreated) these abbreviations can be used:

    d=days, H=hours, M=minutes, S=seconds

1DK&*&d>3,d<1 would show all problems younger than 3 days (d) and older than one day of students from class 1DK


Bookmark often used requests.

Registered user’s data is protected against queries from anonymous users or other registered users.


../<lang>/todo lists the assignments with date/time given and date/time due.


../<lang>/org allows to add, change or delete IDs for School, Field, Teacher, Class and Role. For fields left empty

  • - is used for logged in users
  • a random ID is generated non-logged-in users

Setting role IDs fails, if the role is owned already. Role prefixes of others are italic. These other users can query your done problems.

new will create a new role.

change will change the identification of the current role, i.e. all the problems done will be copied over.

delete will delete the role and all its done problems.

A color can be chosen to more easily see in which role one is.


One level of privacy is via the IDs you choose. How the IDs link to the real things is only know to you. You could use first or last letter of names, add some additional characters, or do some other obfuscation, without compromising an easy mapping to the real things or person for your purpose.

All unregistered users fall into one user category. Therefore every other unregistered user can query all other unregistered users’ problems (non-owned).

A logged-in user assumes ownership of non-owned roles.

If you register and create instances of school, field, teacher, class and student, then they are associated to you as a user (owned). Then you can query all instances below your instance in the hierarchy:

    n Fields
        n Teachers
            n Classes
                n Roles


  • If a teacher role belongs to you, then classes and students that use the same IDs up to and inclusive teacher as your IDs, then you will be able to query them in the done page, even if they belong to some other user.
  • A director in an educational institution could make a School ID. If all teachers use the same School ID, then the director will be able to query the whole hierarchy.

On the other hand, if you start your query above an instance that does not belong to you, you will not see anything below, even if you have instances somewhere in the deeper levels of the hierarchy.

In .../<lang>/done?<school>&<field>&<teacher>&<class>&<role>&<problem> you can drop instances from the left, immediately after the ?. .../<lang>/done?aclass&*&d>2 would query all problems of any student of class aclass not older than 2 days. For this to work aclass needs to belong to you. If it does not, but the teacher role above belongs to your, then you can still query by entering .../<lang>/done?ateacher&aclass&*&d>2.



As I was about to engage in a teaching job in the beginning of 2013 I was looking for a way adequate for our times

  • to follow the progress of my students
  • to automate certain activities

I did not find a finished solution fitting to my ideas, but I found Google AppEngine, which seemed to be a good basis for an own project.

During my teaching job it was still in a very unsophisticated state, but it was usable already. During that time I added mostly problems, some summaries or other texts that did fit into the topics in class.

The first name, mamchecker, came about from this school’s abbreviation of the subject mathematics as MAM.

Since summer 2013 I restructured the code and added user management and I translated the problems and texts into English.

As I did not continue teaching in autumn, my major motivation for the additional effort was to make my initial effort usable for others.


I was kept busy 5+ years by a employment. Now I revisited the project,

  • renamed it to chcko
  • updated it to Python 3 and
  • to the change at Google AppEngine (now part of GCP): ndb changes, no email any more
  • added support for SQL databases using sqlalchemy
  • made it a python package chcko
  • separated the content to a separate chcko-r package, as an example
  • made some fixes

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