473,747 Members | 2,298 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

struct.pack Format String Question

Hello. I am reverse engineering some Python Code. I am using the book
"The Quick Python Book" as an aide.

The following line exists in the code:

msg = struct.pack('BB BB',word0, word1, word2, word3, word4)

In this struct.pack command, the format string is 'BBBB.' In the book,
it gives the following examples for characters that are meaningful to
struct:

'h' - short integer
'd' - double-precision floating point
's' - string

In this case, 'B' is used. What does 'B' represent? What other
characters can be used? Does a list of this exist somewhere?

Thank you for your help.

Josh

Jul 18 '05 #1
2 3678
Joshua Forgione wrote:
In this case, 'B' is used. What does 'B' represent? What other
characters can be used? Does a list of this exist somewhere?


http://www.python.org/doc/current/li...le-struct.html

--
__ Erik Max Francis && ma*@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
\__/ But you're not going to be there tomorrow. And it's all about
tomorrow. -- Montgomery Brogan
Jul 18 '05 #2
"B" is unsigned character (from Python Library Reference).

I'm hoping you copied the line down wrong, because it won't
work (there is probably another B).

See output below:

import struct
word0=1
word1=2
word2=3
word3=4
word4=5
msg = struct.pack('BB BB',word0, word1, word2, word3, word4)
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
error: too many arguments for pack format

Larry Bates
Syscon, Inc.

-------------------------------------------------------

"Joshua Forgione" <jf******@vt.ed u> wrote in message
news:40******** *******@vt.edu. ..
Hello. I am reverse engineering some Python Code. I am using the book
"The Quick Python Book" as an aide.

The following line exists in the code:

msg = struct.pack('BB BB',word0, word1, word2, word3, word4)

In this struct.pack command, the format string is 'BBBB.' In the book,
it gives the following examples for characters that are meaningful to
struct:

'h' - short integer
'd' - double-precision floating point
's' - string

In this case, 'B' is used. What does 'B' represent? What other
characters can be used? Does a list of this exist somewhere?

Thank you for your help.

Josh

Jul 18 '05 #3

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

3
3648
by: Gordon Scott | last post by:
Hi All, I've got a problem I'm seeing when trying to use the struct module to send data to a different machine. Actually I'm making a condensed file that gets transferred to and read on a BREW enabled cell-phone, essentially I'm trying to format content as if it were being streamed over a socket. So I am trying to write a string by first sending a two-byte length of the
0
2303
by: Josiah Carlson | last post by:
Good day everyone, I have produced a patch against the latest CVS to add support for two new formatting characters in the struct module. It is currently an RFE, which I include a link to at the end of this post. Please read the email before you respond to it. Generally, the struct module is for packing and unpacking of binary data. It includes support to pack and unpack the c types: byte, char, short, long, long long, char, *, and...
2
3694
by: Sergey Dorofeev | last post by:
I can use string.unpack if string in struct uses fixed amount of bytes. But is there some extension to struct modue, which allows to unpack zero-terminated string, size of which is unknown? E.g. such struct: long, long, some bytes (string), zero, short, short, short.
16
3000
by: Alfonso Morra | last post by:
Hi, I am at the end of my tether now - after spending several days trying to figure how to do this. I have finally written a simple "proof of concept" program to test serializing a structure containing pointers into a "flattened" bit stream. Here is my code (it dosen't work - compiles fine, pack appears to work, but unpack retrieves jibberish and causes program to crash).
3
2706
by: Chandu | last post by:
In using the following struct format I get the size as 593. The same C struct is 590 if packed on byte boundary and 596 when using pragma pack(4). I am using pack(4) and added 3 spares at the end to get by. hdrFormat = '16s 32s 32s B 8s H 8s H 4s H H 20s 64s 64s 64s 32s 32s 64s L L B B B B B 64s 64s' Any ideas on what I am doing wrong?
10
2275
by: Giovanni Bajo | last post by:
Hello, given the ongoing work on struct (which I thought was a dead module), I was wondering if it would be possible to add an API to register custom parsing codes for struct. Whenever I use it for non-trivial tasks, I always happen to write small wrapper functions to adjust the values returned by struct. An example API would be the following: ============================================
3
4841
by: David Bear | last post by:
I found this simple recipe for converting a dotted quad ip address to a string of a long int. struct.unpack('L',socket.inet_aton(ip)) trouble is when I use this, I get struct.error: unpack str size does not match format I thought ip addresses were unsigned 32 bit integers.
2
3267
by: Tom Plunket | last post by:
I am building a file with the help of the struct module. I would like to be able to put Unicode strings into this file, but I'm not sure how to do it. The format I'm trying to write is basically this C structure: struct MyFile { int magic;
2
10742
by: Jansson Christer | last post by:
Hi all, I have discovered that in my Python 2.4.1 installation (on Solaris 8), struct.pack handles things in a way that seems inconsistent to me. I haven't found any comprehensible documentation over known issues with Python 2.4.1 so I try this... Here's the thing:
0
8979
marktang
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look ! Part I. Meaning of...
0
8818
by: Hystou | last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it. First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
0
9522
Oralloy
by: Oralloy | last post by:
Hello folks, I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>". The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed. This is as boiled down as I can make it. Here is my compilation command: g++-12 -std=c++20 -Wnarrowing bit_field.cpp Here is the code in...
1
9307
by: Hystou | last post by:
Overview: Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
1
6790
isladogs
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules. He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms. Adolph will...
0
4589
by: TSSRALBI | last post by:
Hello I'm a network technician in training and I need your help. I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs. The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols. I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
0
4860
by: adsilva | last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
1
3296
by: 6302768590 | last post by:
Hai team i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
3
2203
bsmnconsultancy
by: bsmnconsultancy | last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.