Parsing info into a 2d list

Bengt Richter bokr at oz.net
Thu Oct 21 03:41:32 CEST 2004


On 20 Oct 2004 13:27:40 -0700, matt.walsh at gmail.com (Matthew Walsh) wrote:

>Whats wrong with the following code?
Why not print out the data it's using as it goes? That's only 5 lines.
There might be a clue.

>using pythonWin I get the following error:
>
>Traceback (most recent call last):
>  File "C:\Python23\Lib\site-packages\pythonwin\pywin\framework\scriptutils.py",
>line 310, in RunScript
>    exec codeObject in __main__.__dict__
>  File "C:\Documents and Settings\Administrator\My
>Documents\file_parser.py", line 16, in ?
>    rownum = range(eval(nrows))
>TypeError: object doesn't support item assignment
>
>>>CODE
>f = open('f:\input.dat')
>feed= f.read()
>lines = feed.split('\n')
>ncols = lines[0].split()[1]
>nrows = lines[1].split()[1]
>xllcorner = lines[2].split()[1]
>yllcorner = lines[3].split()[1]
>cellsize = lines[4].split()[1]
>NoData = lines[5].split()[1]
>
Stylistically, that's a lot of re-typing. E.g., see below for alternative
Also, why not put all those on one line? Or don't you have control over input format?

>colnum = range(eval(ncols))
>rownum = range(eval(nrows))
the best way to convert from string to integer is int(thestring), not eval(thestring).
The latter risks bad surprises if thestring has not been verified safe.
>
>for r in rownum:
>    for c in colnum:
>        slope[r][c]= eval(lines[6+r].split()[c])
What is slope? Nested list representation of 2D array?
what is the format of the items on the line? Presumably numeric literals, but ints? floats?

I'll assume floats would be safe, but I special cased-NoData.

Have you considered making slope a list subclass instance that you can access your
named values from as well as slope[r][c] for data values, and initialize like
f = file('f:\input.dat'); slope = Slope(f) ? E.g., (not tested beyond what you see ;-)

----< slope.py >------------------------
class Slope(list):
    """
    2D data container initialized from text line sequence or iterator yielding:
        ... ncols ...
        ... nrows ...
        ... xllcorner ...
        ... yllcorner ...
        ... cellsize ...
        ... NoData ...
        <row 0>
        <row 1>
        <row nrows-1>
    where a row is
        col0value col1value col2value ... col<ncols-1>value
    If the iterator is an open file, the caller is responsible for closing it. 
    """
    def __init__(self, lines):
        lines = iter(lines)
        for name in 'ncols nrows xllcorner yllcorner cellsize'.split():
            setattr(self, name, int(lines.next().split()[1]))
        self.NoData = lines.next().split()[1]
        mx = []
        for r in xrange(self.nrows):
            mx.append([float(v) for v in lines.next().split()])
        list.__init__(self, mx)
    def __str__(self):
        return '\n'.join(['<Slopes object:']+map(str, list(self))+['>'])

def test():
    mx = Slope("""\
    ?? 3
    ?? 2
    ?? 111
    ?? 222
    ?? 333
    ?? NoDataToken??
    0 1 2
    3 4 5
    """.splitlines())
    for name in 'ncols nrows xllcorner yllcorner cellsize NoData'.split():
        print '%10s: %r' % (name, getattr(mx, name))
    print mx
    for r in xrange(mx.nrows):
        for c in xrange(mx.ncols):
            print mx[r][c],

if __name__ == '__main__':
    test()
----------------------------------------

I put ?? as place holders since I didn't know what you had there.

Result:

[18:39] C:\pywk\clp>slope.py
     ncols: 3
     nrows: 2
 xllcorner: 111
 yllcorner: 222
  cellsize: 333
    NoData: 'NoDataToken??'
<Slopes object:
[0.0, 1.0, 2.0]
[3.0, 4.0, 5.0]
>
0.0 1.0 2.0 3.0 4.0 5.0

Regards,
Bengt Richter



More information about the Python-list mailing list