exercism fetch python variable-length-quantity

Variable Length Quantity

Implement variable length quantity encoding and decoding.

The goal of this exercise is to implement VLQ encoding/decoding.

In short, the goal of this encoding is to encode integer values in a way that would save bytes. Only the first 7 bits of each byte is significant (right-justified; sort of like an ASCII byte). So, if you have a 32-bit value, you have to unpack it into a series of 7-bit bytes. Of course, you will have a variable number of bytes depending upon your integer. To indicate which is the last byte of the series, you leave bit #7 clear. In all of the preceding bytes, you set bit #7.

So, if an integer is between 0-127, it can be represented as one byte. Although VLQ can deal with numbers of arbitrary sizes, for this exercise we will restrict ourselves to only numbers that fit in a 32-bit unsigned integer. Here are examples of integers as 32-bit values, and the variable length quantities that they translate to:

00000000              00
00000040              40
0000007F              7F
00000080             81 00
00002000             C0 00
00003FFF             FF 7F
00004000           81 80 00
00100000           C0 80 00
001FFFFF           FF FF 7F
00200000          81 80 80 00
08000000          C0 80 80 00
0FFFFFFF          FF FF FF 7F

Exception messages

Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message.

To raise a message with an exception, just write it as an argument to the exception type. For example, instead of raise Exception, you should write:

raise Exception("Meaningful message indicating the source of the error")

Running the tests

To run the tests, run the appropriate command below (why they are different):

Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version): python -m pytest variable_length_quantity_test.py

Common pytest options

For other options, see python -m pytest -h

Submitting Exercises

Note that, when trying to submit an exercise, make sure the solution is in the $EXERCISM_WORKSPACE/python/variable-length-quantity directory.

You can find your Exercism workspace by running exercism debug and looking for the line that starts with Workspace.

For more detailed information about running tests, code style and linting, please see the help page.


A poor Splice developer having to implement MIDI encoding/decoding. https://splice.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.