[python] Convert bytes to int?

I'm currently working on an encryption/decryption program and I need to be able to convert bytes to an integer. I know that:

bytes([3]) = b'\x03'

Yet I cannot find out how to do the inverse. What am I doing terribly wrong?

int.from_bytes( bytes, byteorder, *, signed=False )

doesn't work with me I used function from this website, it works well

https://coderwall.com/p/x6xtxq/convert-bytes-to-int-or-int-to-bytes-in-python

def bytes_to_int(bytes):
    result = 0
    for b in bytes:
        result = result * 256 + int(b)
    return result

def int_to_bytes(value, length):
    result = []
    for i in range(0, length):
        result.append(value >> (i * 8) & 0xff)
    result.reverse()
    return result

Lists of bytes are subscriptable (at least in Python 3.6). This way you can retrieve the decimal value of each byte individually.

>>> intlist = [64, 4, 26, 163, 255]
>>> bytelist = bytes(intlist)       # b'@x04\x1a\xa3\xff'

>>> for b in bytelist:
...    print(b)                     # 64  4  26  163  255

>>> [b for b in bytelist]           # [64, 4, 26, 163, 255]

>>> bytelist[2]                     # 26