Append numeric value to binary string

Question

tl;dr: Given x,i = b'', 10, how can I concatenate i onto x, resulting in x == b'\x10'?

I'm trying to encode a number in Python as a varint as a header for a protobuf encoding.

Here's the code I have:

def encode_varint(value):
    buf = b''
    while True:
        byte = value & 0x7f
        value >>= 7
        if value:
            buf += chr(byte | 0x80)
        else:
            buf += chr(byte)
            break
    return buf

However, this fails because I cannot append a string to bytes.

How do I efficiently take an integer value and append it to a binary string?

The only option I've gotten that 'works' is buf += chr(byte).encode('ascii'), but that does not smell efficient. — Phrogz
– Phrogz, Commented Dec 2, 2016 at 21:56

Phrogz · Accepted Answer · 2016-12-02 22:06:22Z

1

# option 1 (reportedly slower)
buf = b''
buf += bytes([byte])

# option 2 (reportedly faster)
buf = bytearray()
buf.append(byte)

answered Dec 2, 2016 at 22:06

Phrogz

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