Greetings:
I am implementing a (crude but useful) debug facility in my test system client
software. Basically, I test the value of a global Boolean. It True, I write
pertinent data to a text file. I want to do this in multiple functions in a
module. Rather than open and close the file each time I write, I want to open
the file once at the start of process and close it at the end. Here are
excerpts from the module.
##########################
import socket
import struct
import time
# initialize the debug flag
DEBUG = True
. . .
dbgf = None # File object and path for saving debug output
dbgfname = "debug.txt"
def snd_cmd(sock,cmd):
. . .
while remainlen > 0:
if remainlen > MTU:
pktstp = pktstrt + MTU
else:
pktstp = pktlen
pktflags |= EOD
pkthdr = struct.pack('@2BH',pktflags,seq,pktlen)
sndpkt = pkthdr+cmd[pktstrt:pktstp]
if DEBUG:
dbgf.write("command: " + cmd + "\n")
dbgf.write("flags: 0x%X, seq: %u, len: %u\n" % (pktflags, seq,
pktlen))
sock.sendto(sndpkt,addr)
pktstrt += MTU
remainlen -= MTU
pktflags = pktflags & ~SOD
seq = (seq + 1) % 256
. . .
def recv_resp(sock):
response = ''
try:
response = sock.recv(MTU)
except socket.timeout:
errtupl = ("ERROR", 'Server did not respond')
return (errtupl, response)
. . .
if DEBUG:
dbgf.write("response: " + response + "\n")
dbgf.write("flags: 0x%X, seq: %u, len: %u\n" % (flags, retseq, dlen))
. . .
return (errtupl, response)
def do_cmd(cmd):
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.settimeout(timetowait)
retriesleft = retries
if DEBUG:
dbgf = open(dbgfname,mode="a")
dbgf.write("\n"+str(time.localtime())+"\n")
while retriesleft > 0:
snd_cmd(sock, cmd)
recvtupl = recv_resp(sock)
if recvtupl[0][0] != "ERROR":
break
retriesleft -= 1
if DEBUG:
dbgf.close()
sock.close( )
return recvtupl
##########################
When I run this code, I get the following error message:
<<<<<<<<<<<<<<<<<<<<<<<
A problem occurred in a Python script. Here is the sequence of function calls
leading up to the error, in the order they occurred.
/var/www/cgi-bin/pagen.py
76 # function. Check the returned error code for success.
77 cmdtosnd = state['s']['getcmd']
*****78 (errorcode, errorstr), platformstate['itype']['curstate'] =
do_cmd(cmdtosnd)
79 if errorcode == 0:
80 cmdtosnd = state['t']['getcmd']
. . .
/var/www/cgi-bin/Client.py in do_cmd(cmd='cmd')
160
161 while retriesleft > 0:
*****162 snd_cmd(sock, cmd)
163 recvtupl = recv_resp(sock)
164 if recvtupl[0][0] != IIPSRVERROR:
global snd_cmd = <function snd_cmd>, sock = <socket._socketobject object>, cmd
= 'cmd'
/var/www/cgi-bin/Client.py in snd_cmd(sock=<socket._socketobject object>,
cmd='cmd')
65
66 if DEBUG:
*****67 dbgf.write("command: " + cmd + "\n")
69
global dbgf = None, dbgf.write undefined, cmd = 'cmd'
AttributeError: 'NoneType' object has no attribute 'write'
args = ("'NoneType' object has no attribute 'write'",)
>>>>>>>>>>>>>>>>>>>>>>>
dbgf is declared at the top of the module. It is opened and closed in do_cmd.
I attempt to write to it in snd_cmd and recv_resp, both of which are called by
do_cmd. Since dbgf is global to all of these functions, I expected its value
(the open file object) to persist. I don't understand why it didn't. I expect
I have misunderstood Python's scoping rules. Can someone enlighten me?
Thanks and enjoy the holidays.
BGC
________________________
"Never trust anything that can think for itself
if you can't see where it keeps its brain"
JK Rowling
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