Here is some code which uses my pigpio library to monitor the data and clocks.

It assumes you are using standard shift register signal levels.

Three values are printed per latch.

1. the number of bits
2. the data assuming most significant bit first format
3. the data assuming least significant bit first format

#!/usr/bin/env python

# shiftIn.py
# 2016-03-27
# Public Domain

import time

import pigpio # http://abyz.co.uk/rpi/pigpio/python.html

DATA=23
DATACLK=24
RCLK=25

bit = 0
val = 0
nbits = 0

def cbf(g, l, t):
   global bit, val, nbits
   if g == DATA:
      bit = l
   elif g == DATACLK:
      nbits += 1
      val <<= 1
      val |= bit
   elif g == RCLK:
      val2 = 0
      for i in range(nbits):
         if val & (1<<i):
            val2 |= (1<<(nbits-i-1))
      print(nbits, val, val2)
      nbits = 0
      val = 0

pi = pigpio.pi()

if not pi.connected:
   exit(0)

cb1 = pi.callback(DATA, pigpio.EITHER_EDGE, cbf)
cb2 = pi.callback(DATACLK, pigpio.RISING_EDGE, cbf)
cb3 = pi.callback(RCLK, pigpio.FALLING_EDGE, cbf)

time.sleep(600)

cb1.cancel()
cb2.cancel()
cb3.cancel()

pi.stop()

Here is some code which uses my pigpio library to monitor the data and clocks.

It assumes you are using standard shift register signal levels.

Three values are printed per latch.

1. the number of bits
2. the data assuming most significant bit first format
3. the data assuming least significant bit first format

#!/usr/bin/env python

# shiftIn.py
# 2016-03-27
# Public Domain

import time

import pigpio # http://abyz.me.uk/rpi/pigpio/python.html

DATA=23
DATACLK=24
RCLK=25

bit = 0
val = 0
nbits = 0

def cbf(g, l, t):
   global bit, val, nbits
   if g == DATA:
      bit = l
   elif g == DATACLK:
      nbits += 1
      val <<= 1
      val |= bit
   elif g == RCLK:
      val2 = 0
      for i in range(nbits):
         if val & (1<<i):
            val2 |= (1<<(nbits-i-1))
      print(nbits, val, val2)
      nbits = 0
      val = 0

pi = pigpio.pi()

if not pi.connected:
   exit(0)

cb1 = pi.callback(DATA, pigpio.EITHER_EDGE, cbf)
cb2 = pi.callback(DATACLK, pigpio.RISING_EDGE, cbf)
cb3 = pi.callback(RCLK, pigpio.FALLING_EDGE, cbf)

time.sleep(600)

cb1.cancel()
cb2.cancel()
cb3.cancel()

pi.stop()