On 1/16/07, Dave Kuhlman [EMAIL PROTECTED] wrote:
On Tue, Jan 16, 2007 at 11:28:49AM -0500, Joe Abbey wrote:
Hello,
I'm using Active Python v2.4.3.11 on a Windows XP machine.
Probably more relevant is that I'm just learning Python, as in I've been
writing Python for less than 24 hours.
While trying to implement a PE parser, I ran into the following problem:
#** START CODE***
data = file.read(128);
directoryTable = struct.unpack('',
data);
i=0;
print Export table 0x%08X + 0x%08x % (directoryTable[i+=1],
directoryTable[i+=1]);
print Import table 0x%08X + 0x%08x % (directoryTable[i+=1],
directoryTable[i+=1]);
#** END CODE***
This code throws a syntax error at the first i+=1 on line 4.
Why is this the case?
In Python, i += 1 is a statement. You have used in as an
expression. In Python, an expression returns a value; a statement
does not.
It seems like it would be very useful to be able to increment an index
after
referencing into an array.
What you are asking for is viewed by some as useful. But, I think
it is too confusing. Should the variable be incremented before or
after it is used to index into the array? C/C++ gives you a
choice: you can use either i++ or ++i, which makes code harder
to read, I think. And, what about:
x = y[i+=1] + z[i]
Has the second use of i been incremented or not.
Is my approach busted? Is there a better way to reference elements?
Instead of:
x = directoryTable[i] + directoryTable[i+=1]);
use something like:
x = directoryTable[i] + directoryTable[i+1]
And, by the way, you do not need all those semicolons at the end of
each line. In Python, the semicolon is a statement separator, not
a statement terminator. It is more Pythonic to use a semicolon
between statements only when there are more than one statement on a
line. And writing more than one statement on a line is usually
discouraged anyway.
The fix I'm currently using is to write the index I want:
(directoryTable[0], directoryTable[1])
Or, if you need an index variable:
directoryTable[i], directoryTable[i+1])
Dave
--
Dave Kuhlman
http://www.rexx.com/~dkuhlman
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Thank you Danny for the iterator tutorial. I'll check the link.
Thanks Dave for the language lesson. As you could tell from my code
snippet, C\C++ is what I have programmed the most in.
For this case I believe the iterator example would be most preferred.
#** START CODE***
dTable = iterator(directoryTable)
print Export table 0x%08X + 0x%08x % (dTable.next(), dTable.next
())
#** END CODE***
But for now the explicit indexing will work fine :)
Thanks!
Joe
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