Conversion of perl unpack code to python - something odd

[Andrew Robert]

Hey everyone,


Maybe you can see something I don't.

I need to convert a working piece of perl code to python.

The perl code is:

sub ParseTrig {
# unpack the ibm struct that triggers messages.
my $struct = shift;

my %data;
@data{qw/StructID Version QName ProcessName TriggerData ApplType
ApplId EnvData UserData QMgrName/} =
unpack("A4A4A48 A48A64A4A256A12 8A128A48", $struct);

return undef unless $data{StructID} eq 'TMC';

return \%data;


Taking away the fact that it is a function, the base code sets a 732
element structure with the ascii pattern derived above.

I wrote a simple test script that accepts the command argument at
position 1.



#!C:\Python24\p ython
import sys, string, struct

# From the language declarations in manual, the following format was derived

format='4s 4s 48s 48s 64s 4s 256s 128s 128s 48s'
size=struct.cal csize(format)

# Extract list item out for convenience/readability
data=sys.argv[1]

# Calculated size of the struct format is 732
# Length of data string is 732

print len(data)
print size

d1,d2=struct.un pack(format,dat a)
print d1
sys.exit(0)


When I run it, it says there are too many values to unpack.



Traceback ( most recent call last)
File "m:\mq\mq\scrip ts\format.py", line 32, in ?
d1, d2 = struct.unpack(f ormat,data)
ValueError: too many values to unpack
Error starting triggered application




I checked the manual on the structure used to pack the code and it
appears correct.

#
# MQTMC2 Language declarations as defined chapt 22 of programmers ref
# http://publibfp.boulder.ibm.com/epubs/pdf/csqzak09.pdf
#
# CHAR4 Struct ID
# CHAR4 Version
# CHAR48 QName
# CHAR48 ProcessName
# CHAR64 TriggerData
# CHAR4 ApplType
# CHAR256 ApplID
# CHAR128 EnvData
# CHAR128 UserData
# CHAR48 QMgrName


Any help you can provide on this would be greatly appreciated.

[Fredrik Lundh]

Re: Conversion of perl unpack code to python - something odd

Andrew Robert wrote:
[color=blue]
> # From the language declarations in manual, the following format was derived
>
> format='4s 4s 48s 48s 64s 4s 256s 128s 128s 48s'[/color]

that's 10 specifiers.
[color=blue]
> d1,d2=struct.un pack(format,dat a)[/color]

that's two variables.
[color=blue]
> print d1
> sys.exit(0)
>
> When I run it, it says there are too many values to unpack.
>
> Traceback ( most recent call last)
> File "m:\mq\mq\scrip ts\format.py", line 32, in ?
> d1, d2 = struct.unpack(f ormat,data)
> ValueError: too many values to unpack
> Error starting triggered application
>
> I checked the manual on the structure used to pack the code and it
> appears correct.[/color]

try printing the return value from struct.unpack, and see if you can
figure out what's wrong with your code:

print struct.unpack(f ormat,data)

</F>

[Peter Otten]

Re: Conversion of perl unpack code to python - something odd

Andrew Robert wrote:
[color=blue]
> format='4s 4s 48s 48s 64s 4s 256s 128s 128s 48s'[/color]

You are trying to squeeze 10 items into just
[color=blue]
> d1,d2=struct.un pack(format,dat a)[/color]

two variables (d1 and d2)
[color=blue]
> ValueError: too many values to unpack[/color]

and Python is quite explicit that it doesn't like that once you realize that
'unpack' doesn't refer to struct.unpack() but to tuple unpacking like
[color=blue][color=green][color=darkred]
>>> a, b = "ab"
>>> a, b = "abc"[/color][/color][/color]
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: too many values to unpack


Peter

[Andrew Robert]

Re: Conversion of perl unpack code to python - something odd

Peter Otten wrote:[color=blue]
> Andrew Robert wrote:
>[color=green]
>> format='4s 4s 48s 48s 64s 4s 256s 128s 128s 48s'[/color]
>
> You are trying to squeeze 10 items into just
>[color=green]
>> d1,d2=struct.un pack(format,dat a)[/color]
>
> two variables (d1 and d2)
>[color=green]
>> ValueError: too many values to unpack[/color]
>
> and Python is quite explicit that it doesn't like that once you realize that
> 'unpack' doesn't refer to struct.unpack() but to tuple unpacking like
>[color=green][color=darkred]
>>>> a, b = "ab"
>>>> a, b = "abc"[/color][/color]
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> ValueError: too many values to unpack
>
>
> Peter
>[/color]
Now I feel like a first class idiot.

Thanks for the help.

Added the extra eight variables and things worked perfectly.

Going to go stand in the corner for an hour now :)