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 are 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:
NUMBER VARIABLE QUANTITY 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
Sometimes it is necessary to raise an exception. When you do this, you should always 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. For situations where you know that the error source will be a certain type, you can choose to raise one of the built in error types, but should still include a meaningful message.
This particular exercise requires that you use the raise statement to "throw" a
ValueError if the sequence to decode or encode is incomplete. The tests will only pass if you both
exception and include a message with it.
To raise a
ValueError with a message, write the message as an argument to the
# if the sequence is incomplete raise ValueError("incomplete sequence")
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