On Aug 20, 5:08 pm, Matthias Güntert <matzeguent...@gmx.de> wrote:
> Hello guys
>
> I would like to read a hex number from an ASCII file, increment it and
> write it back.
> How can this be performed?
>
> I have tried several approaches:
>
> my file serial.txt contains: 0C
>
> ----------------------------------
> f = open('serial.txt', 'r')
> val = f.read()
> val = val.encode('hex')
> print val
> ----------------------------------
> --> 3043
>
> ----------------------------------
> f = open('serial.txt', 'r')
> val = f.read()
> print val
> val = val+1
> ----------------------------------
> --> TypeError: cannot concatenate 'str' and 'int' objects
>
> ----------------------------------
> f = open('serial.txt', 'rb')
> val = f.read()
> val = val + 1
> ----------------------------------
> --> TypeError: cannot concatenate 'str' and 'int' objects
>
> hm....
Check this out:
In [1]: val = '0C'
In [2]: val.encode('hex')
Out[2]: '3043'
That's not what you want. Try this:
In [3]: int(val, 16)
Out[3]: 12
And to convert an int to a hex string.
In [4]: '%x' % 13
Out[4]: 'd'
The interpreter has a help() function that gives you quick access to
information about python objects:
>>> help(str.encode)
Help on method_descriptor:
encode(...)
S.encode([encoding[,errors]]) -> object
Encodes S using the codec registered for encoding. encoding
defaults
to the default encoding. errors may be given to set a different
error
handling scheme. Default is 'strict' meaning that encoding errors
raise
a UnicodeEncodeError. Other possible values are 'ignore',
'replace' and
'xmlcharrefreplace' as well as any other name registered with
codecs.register_error that is able to handle UnicodeEncodeErrors.
>>> help(int)
Help on class int in module __builtin__:
class int(object)
| int(x[, base]) -> integer
|
| Convert a string or number to an integer, if possible. A floating
point
| argument will be truncated towards zero (this does not include a
string
| representation of a floating point number!) When converting a
string, use
| the optional base. It is an error to supply a base when
converting a
| non-string. If the argument is outside the integer range a long
object
| will be returned instead.
|
| Methods defined here:
|
...
Unfortunately you can't use it on the '%' string formatting
operator...
>>> help(%)
SyntaxError: invalid syntax
So here's a link to the docs:
http://docs.python.org/library/stdtypes.html#string-formatting-operations
HTH,
~Simon
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