It’s a tad bit clunky, but you need to use the stdout buffer:
python3 -c "import sys; sys.stdout.buffer.write(b'A'*5 + b'\xde\xad\xc0\xde')" | xxd
00000000: 4141 4141 41de adc0 de AAAAA....
When using pwntools, you usually don’t need to care about the encoding back and forth, though. The tubes accept byte strings, by default. That way, you can (transparently) send binary data to a process’ stdin, a network socket, or whatever you need to communicate with.
E.g. for locally testing/developing an exploit, you can use something like:
from pwn import *
REMOTE=False # switch to True, once your exploit works locally
if REMOTE:
p = remote('vulnservice.web', 1234)
else:
p = process('./vuln-binary')
banner = p.read(1024)
buffer = b'A'*5 # padding to reach overflow
buffer += b'\xde\xad\xc0\xde' # return address of JMP ESP in glibc
buffer += fancy_shellcode
p.send(buffer)
...