buffer interface problem

[Andrew Gillanders]

I have run into a problem running a Python script that is part of the
TerraGear suite for building scenery for FlightGear. I am using Mac
OS X 10.4, running Python (version 3.0.1) in a Unix terminal.

The purpose of the script is to walk a directory tree, unzipping
files, and passing the contents to an executable C programme. The
problem occurs here:

gzin = GzipFile(fname, 'rb')
data = gzin.readline()
min_x,min_y = map(atoi,data.split()[:2])

The input file, when uncompressed, is an ASCII file with a line with
two numbers, then a line of four numbers, then many long lines of
numbers. I can see what the last is trying to do: split the string
into two words, convert them to integers, and assign them to min_x
and min_y.

At the third line, I get the message "expected an object with the
buffer interface". Which object is it referring to? Have some
functions been changed to pass buffer objects instead of strings? How
can I fix the source code to make it run?

Any help appreciated
Andrew
(Python newbie)

[Chris Rebert]

On Thu, Jan 7, 2010 at 12:19 AM, Andrew Gillanders
<andrew.g...@uqconnect.edu.au> wrote:
> I have run into a problem running a Python script that is part of the
> TerraGear suite for building scenery for FlightGear. I am using Mac OS X
> 10.4, running Python (version 3.0.1) in a Unix terminal.
>
> The purpose of the script is to walk a directory tree, unzipping files, and

> passing the contents to an executable C program. The problem occurs here:

>
>    gzin = GzipFile(fname, 'rb')
>    data = gzin.readline()
>    min_x,min_y = map(atoi,data.split()[:2])
>
> The input file, when uncompressed, is an ASCII file with a line with two
> numbers, then a line of four numbers, then many long lines of numbers. I can
> see what the last is trying to do: split the string into two words, convert
> them to integers, and assign them to min_x and min_y.
>
> At the third line, I get the message "expected an object with the buffer
> interface". Which object is it referring to?

The elements of the list produced by `data.split()[:2]`, which are
either Unicode strings or bytestrings, neither of which are buffers.

> Have some functions been
> changed to pass buffer objects instead of strings? How can I fix the source
> code to make it run?

The error is being raised by the atoi() function (in the future,
please post the full Traceback, not just the final error message).
What module/library does your atoi() function come from (look for an
`import` statement mentioning it)?
The only functions by that name in the Python standard library both
operate on strings, not buffers, and thus can't be the same one your
code is using.

In any case, replacing `atoi` with `int` in your code will likely
solve the problem. The built-in int() function* can convert strings to
integers.

Cheers,
Chris
--
http://blog.rebertia.com

*Not really a function, but close enough for newbie explanatory purposes.

[Andrew Gillanders]

Thanks Chris. The atoi function was coming from the locale library
(from locale import atoi). I changed it to int and now it works.

The next hurdle is this:

gzin = GzipFile(fname, 'rb')

data = gzin.readline()
# min_x,min_y = map(atoi,data.split()[:2])
min_x,min_y = map(int,data.split()[:2])

data = gzin.readline()
# span_x,step_x,span_y,step_y = map(atoi,data.split()[:4])
span_x,step_x,span_y,step_y = map(int,data.split()[:4])

data = gzin.read().split('\n')

The last line is a problem, giving me this message: Type str doesn't
support the buffer API (I am guessing a conflict between split and
read?)

Sorry, I am new to Python, so how do I get a Traceback?

Thanks
Andrew

[Chris Rebert]

On Thu, Jan 7, 2010 at 4:47 AM, Andrew Gillanders

> Thanks Chris. The atoi function was coming from the locale library (from

> locale import atoi). I changed it to int and now it works.

Hm, that's odd since it was one of the 2 functions in the std lib
which the docs say operates on strings...

> The next hurdle is this:
> gzin = GzipFile(fname, 'rb')
>
> data = gzin.readline()
> # min_x,min_y = map(atoi,data.split()[:2])
> min_x,min_y = map(int,data.split()[:2])
>
> data = gzin.readline()
> # span_x,step_x,span_y,step_y = map(atoi,data.split()[:4])
> span_x,step_x,span_y,step_y = map(int,data.split()[:4])
>
> data = gzin.read().split('\n')
>
> The last line is a problem, giving me this message: Type str doesn't support
> the buffer API (I am guessing a conflict between split and read?)

Ah, looking at the 3.0 docs on buffers, I'd surmise gzin.read()
returns bytes (http://docs.python.org/3.1/library/functions.html#bytes)
rather than a string.
You'll want to decode the bytes into characters first, and then you
can operate on the resulting string normally.
Try:

data = gzin.read().decode('ascii').split('\n')

> Sorry, I am new to Python, so how do I get a Traceback?

You should get one by default. Are you running the script in some
environment other than the command line?

Here's what a traceback looks like:

Traceback (most recent call last):
File "foo", line 161, in <module>
main()
File "foo.py", line 157, in main
bot.run()
File "foo.py", line 68, in bar
self.baz("Enter number: ")
File "foo.py", line 112, in baz
choice = int(raw_input(prompt))-1
ValueError: invalid literal for int() with base 10: 'y'