Python: read and write binary files

def copy(if_path, of_path):
    with open(if_path, 'rb') as in_file, open(of_path, 'wb') as out_file:
        while True:
            chunk = in_file.read(1024)
            if chunk:
                out_file.write(chunk)
                out_file.flush()
            else:
                break

Python: mutable byte array as buffer

bytearray function can be used to make a mutable byte array as buffer:

import struct
buffer = bytearray(8)
buffer[0]=1
buffer[1]=1
struct.pack_into('>ih', buffer, 2, 100, 200)
# to convert the array to str
print(bytes(buffer))

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see also

• struct.unpack_into

python: join lists

list1 = ['a', 'b']
list2 = ['c', 'd']

list3 = list1 + list2

Python: encode integers to byte string

import struct
def int_to_bytes(value, size, big_endian=False):
    bs = []
    for i in range(size):
        offset = i * 8
        b = chr((value & (0xff << offset)) >> offset)
        if big_endian:
            bs.insert(0, b)
        else:
            bs.append(b)
    return b''.join(bs)

def int32_to_bytes(value, big_endian=False):
    return int_to_bytes(value, 4, big_endian)

def int64_to_bytes(value, big_endian=False):
    return int_to_bytes(value, 8, big_endian)

if __name__ == '__main__':
    # the two commands below do the same
    print(repr(int64_to_bytes(65536, big_endian=True)))
    print(repr(struct.pack('>Q', 65536)))

---

see also

• Python: struct.pack

python: print a string as hex bytes

':'.join(x.encode('hex') for x in 'Hello World!')

---

Executes in python CLI:

>>> ':'.join(x.encode('hex') for x in 'Hello World!')
'48:65:6c:6c:6f:20:57:6f:72:6c:64:21'

join binary strings in Python

b''.join(['abc', '\x01\x02\x03', 'efg'])

---

Execute it in python cli:

>>> b''.join(['abc', '\x01\x02\x03', 'efg'])
'abc\x01\x02\x03efg'

Python: get the length of a utf-8 encoded string

len(s.encode('utf-8'))