Pfthb

I have the following code:

from BitVector import BitVector
import struct
import ipaddress

def run_marker_function(marker):
 bv = BitVector(size=16) # 16 0s
 m(bv, "27.246.2.177", "255.255.255.0")

def m(bv, R, R1):
 # converts ipaddr strings to binary
 bitForm = bin(int(ipaddress.IPv4Address(R)))[2:]
 bitForm1 = bin(int(ipaddress.IPv4Address(R1)))[2:]
 # R2 helper fn is the interleaved output of the 32 bit IP addresses in binary form (R2 is 64 bits)
 R2 = Interleaved(bitForm, bitForm1)
 # splits R2 into list of 8 items, each 8 bits
 frags = [R2[i:i+8] for i in range(0, len(R2), 8)]
 o = 3
 f = frags[o]
 # bv[0:3] = 000 initially, I increment by o
 offset = bv[0:3].int_val() + o
 bv[0:3] = BitVector(intVal=offset, size=3)
 # bv[8:16] = 00000000 initially, I want to replace with the 8 bits of f - DOESN'T WORK
 frag = bv[8:16].int_val() + int(f,2)
 bv[8:16] = BitVector(intVal=frag, size=len(bv[8:16]))

and I get the following error:

 18 frag = bv[8:16].int_val() + int(f,2)
---> 19 bv[8:16] = BitVector(intVal=frag, size=len(bv[8:16]))

/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/BitVector/BitVector.py in __init__(self, *args, **kwargs)
else:
 if size < len(bitlist):
 raise ValueError('''The value specified for size must be at least as large as for the smallest bit vector possible for intVal''')

ValueError: The value specified for size must be at least as large as for the smallest bit vector possible for intVal

But I don't understand why as I'm putting in the actual length of that splice of the bv. Also, I'm doing the same methodology in

offset = bv[0:3].int_val() + o
bv[0:3] = BitVector(intVal=offset, size=3)

which doesn't throw an error

EDIT
A similar instance of the same bug:

dist = bv[3:8].int_val() + 1
bv[3:8] = BitVector(intVal=dist, size=1)

Gives the error

/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/BitVector/BitVector.py in __setitem__(self, pos, item)
 if ( (pos.stop - pos.start) != len(item) ):
 raise ValueError('incompatible lengths for slice assignment 7')
 for i in range( pos.start, pos.stop ):
 self[i] = item[ i - pos.start ]

ValueError: incompatible lengths for slice assignment 7