So I'm trying to read the block files with Python.

From this link, What are the keys used in the blockchain levelDB (ie what are the key:value pairs)?, it tells you how to access the files with leveldb. So I wrote a class to read in the meta data.

class ReadBytes:
    def __init__(self, bytes):
        self.posistion = 0
        self.bytes = bytes

    def get_int(self, byte_count):
        self.posistion += byte_count
        return decode(self.bytes[self.posistion - byte_count:self.posistion][::-1], 256)

    def get_var_int(self):
        self.posistion += 1
        value = byte_to_int(self.bytes[self.posistion - 1])
        if value < 253:
            return value
        return self.get_int(pow(2, value - 252))

But from this link, https://github.com/bitcoin/bitcoin/blob/master/src/chain.h#L364, It turns out there is this thing call VarIntMode::NONNEGATIVE_SIGNED that is tripping me up. I can read regular var int with my Python class, but how do I read the non-negative signed ones in Python?

1 Answer 1


A non-negative signed varint is just a normal varint but should be put into a signed integer rather than an unsigned integer as with normal varints. You just need to also check that it is a non-negative integer.

For example, instead of decoding a 32 bit varint as a uint32_t, you decode it as int32_t and check that it's value is >= 0.

Your code looks like it is decoding things as signed integers already. Instead of using Python's conversions built into the various classes, I recommend that you use the struct module so that you can specify endianness and signedness of the bytes that you are decoding.

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