Python - 如何生成长、固定长度、有效的字节字符串？

Question

I'm trying to create a socket-based client which can send simulated Call Records to a receiver. The socket client is complete, now I need to work on the payload generator. The call record looks like this:

CDR = b'173600009                   3052      334088888                   1001   0    #500 0         00000000 0          0    \r\n\x00\x00\x00'

Each space is counted, meaning that each bit in this string belongs to a "field" Spaces just mean no data for that particular field.

I'm looking for a proper way to generate records like this, but make it simple enough where I can specify a range of values for each field.

Basically:

timestamp = CDR[0:4]
call_party = CDR[12:18]

... etc

then something like

for i in [list_of_call_party]:
  call_party = i

finally:

join( timestamp, call_party, etc), etc to create a new VALID record of the proper length.

I just need a nudge in the right direction to make this Call record generator.

Thanks!

Answer 1

The easiest way is probably an encode method...

def encode(timestamp=0, ...):
    return '%-*s...' % 4, timestamp, ...

You can add a method for decode as well...

def decode(msg):
    return msg[0:4], ...