def _int2bytes(number, block_size=None):
"""Converts a number to a string of bytes.
Usage::
>>> _int2bytes(123456789)
b'\x07[\xcd\x15'
>>> bytes2int(_int2bytes(123456789))
123456789
>>> _int2bytes(123456789, 6)
b'\x00\x00\x07[\xcd\x15'
>>> bytes2int(_int2bytes(123456789, 128))
123456789
>>> _int2bytes(123456789, 3)
Traceback (most recent call last):
...
OverflowError: Needed 4 bytes for number, but block size is 3
@param number: the number to convert
@param block_size: the number of bytes to output. If the number encoded to
bytes is less than this, the block will be zero-padded. When not given,
the returned block is not padded.
@throws OverflowError when block_size is given and the number takes up more
bytes than fit into the block.
"""
# Type checking
if not is_integer(number):
raise TypeError("You must pass an integer for 'number', not %s" %
number.__class__)
if number < 0:
raise ValueError("Negative numbers cannot be used: %i" % number)
# Do some bounds checking
if number == 0:
needed_bytes = 1
raw_bytes = [b"\x00"]
else:
needed_bytes = common.byte_size(number)
raw_bytes = []
# You cannot compare None > 0 in Python 3x. It will fail with a TypeError.
if block_size and block_size > 0:
if needed_bytes > block_size:
raise OverflowError("Needed %i bytes for number, but block size "
"is %i" % (needed_bytes, block_size))
# Convert the number to bytes.
while number > 0:
raw_bytes.insert(0, byte(number & 0xFF))
number >>= 8
# Pad with zeroes to fill the block
if block_size and block_size > 0:
padding = (block_size - needed_bytes) * b"\x00"
else:
padding = b""
return padding + b"".join(raw_bytes)
def assert_int(var, name):
"""Asserts provided variable is an integer."""
if is_integer(var):
return
raise TypeError('%s should be an integer, not %s' % (name, var.__class__))