Retrieving int from hex in a file.

[Filipe Teixeira]

Hi.

I have to open a binary file from an old computer and recover the
information stored (or at least try to). I use:

f=open('file.bi n','rb')
a=f.read()
f.close()

a in now a string full of hex representations in the form:

a[6]='\x14'
a[7]='\x20'

I would like to convert these hex representations to int, but this
(the most obvious way) doesn't seem to be working

>>q=a[6]
q

'\x14'

>>int(q,16)

Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: invalid literal for int():

>>>

How can I do this?

Thanks

[Gabriel Genellina]

En Mon, 28 Apr 2008 07:14:51 -0300, Filipe Teixeira <fi*******@gmai l.comescribió:

a in now a string full of hex representations in the form:

a[6]='\x14'
a[7]='\x20'

I would like to convert these hex representations to int, but this
(the most obvious way) doesn't seem to be working

>>>q=a[6]
q

'\x14'

>>>int(q,16)

Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: invalid literal for int():

>>>>

Use ord(q)

pyhelp(ord)
Help on built-in function ord in module __builtin__:

ord(...)
ord(c) -integer

Return the integer ordinal of a one-character string.

py>

--
Gabriel Genellina

[Peter Otten]

Filipe Teixeira wrote:

I have to open a binary file from an old computer and recover the
information stored (or at least try to). I use:

I would like to convert these hex representations to int, but this

If you want to do it efficiently have a look at the array module:

>>import os, array
a = array.array("B" )
filename = "/usr/bin/python"
a.fromfile(op en(filename, "rb"), os.path.getsize (filename))
a[10]

0

>>a[:10]

array('B', [127, 69, 76, 70, 2, 1, 1, 0, 0, 0])

Peter

[bgeddy]

Filipe Teixeira wrote:

Hi.

I have to open a binary file from an old computer and recover the
information stored (or at least try to). I use:

f=open('file.bi n','rb')
a=f.read()
f.close()

a in now a string full of hex representations in the form:

a[6]='\x14'
a[7]='\x20'

I would like to convert these hex representations to int, but this
(the most obvious way) doesn't seem to be working

>>>q=a[6]
q

'\x14'

>>>int(q,16)

Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: invalid literal for int():

How can I do this?

Thanks

As you say you are trying to recover information from the old computer
are you sure you want to convert the data to it's integer representation ?
What I mean is in this case the string will contain the actual data read
from the file, not a hex representation. It's just the python displays
this data as '\x14'. BTW - are you sure it's displaying '\x20' from your
data as this should be a space character i.e. " ".

In the python interpreter try this:

mydata=""
for i in range(256):
mydata+=chr(i)

>mydata

This will show you the hex representation of the values in mydata that
it can't display however the string is not a string of "hex values" as
such, it contains the binary values 0-255.

[Filipe Teixeira]

>

Use ord(q)

pyhelp(ord)
Help on built-in function ord in module __builtin__:

ord(...)
ord(c) -integer

Return the integer ordinal of a one-character string.

py>

--
Gabriel Genellina

Thank you Gabriel. It fit's my purpose.

[Grant Edwards]

On 2008-04-28, Filipe Teixeira <fi*******@gmai l.comwrote:

Hi.

I have to open a binary file from an old computer and recover the
information stored (or at least try to). I use:

f=open('file.bi n','rb')
a=f.read()
f.close()

a in now a string full of hex representations in the form:

a[6]='\x14'
a[7]='\x20'

a is now a string of binary data. It doesn't contain a "hex
representation" of anything. Hex is a way of printing stuff on
paper or on a screen. Python doesn't store anything in hex.

I would like to convert these hex representations to int,

That's your mistake: you don't have hex data. Nothing is being
stored in hex in your example.

but this (the most obvious way) doesn't seem to be working

>>>q=a[6]
q

'\x14'

>>>int(q,16)

That converts a hex string into an integer, you've not got a
hex string. You have a string containing binary data.

"4A4B4C" is a hex string. It's 6 bytes long and contains the
ASCII characters '4' 'A' '4' 'B' '4' 'C'.

"\x4a\x4b\4 c" is just a three-byte long chunk of binary data.
It was _typed_ in hex, but it's stored in binary not in hex.
It's identical to "JKL".

Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: invalid literal for int():

>>>>

How can I do this?

You can use the struct module, or you can do it explicitly like
this:

>>a = 'abcdef\x12\x34 qwer'
n = (ord(a[6])<<8) | ord(a[7])
n

4660

>>hex(n)

'0x1234'

>>>

--
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at PH.D. will you get able to
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