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Trash: Cookbook String list processing

Brian Granger edited this page · 1 revision
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String lists are handy way to process output from system commands.

First, we acquire the output of 'ls -l':

[Q:doc/examples]|2> lines = !ls -l
 ==
['total 23',
 '-rw-rw-rw- 1 ville None 1163 Sep 30  2006 example-demo.py',
 '-rw-rw-rw- 1 ville None 1927 Sep 30  2006 example-embed-short.py',
 '-rwxrwxrwx 1 ville None 4606 Sep  1 17:15 example-embed.py',
 '-rwxrwxrwx 1 ville None 1017 Sep 30  2006 example-gnuplot.py',
 '-rwxrwxrwx 1 ville None  339 Jun 11 18:01 extension.py',
 '-rwxrwxrwx 1 ville None  113 Dec 20  2006 seteditor.py',
 '-rwxrwxrwx 1 ville None  245 Dec 12  2006 seteditor.pyc']

Now, let's take a look at the contents of 'lines' (the first number is the list element number):

[Q:doc/examples]|3> lines
                <3> SList (.p, .n, .l, .s, .grep(), .fields() available). Value:

0: total 23
1: -rw-rw-rw- 1 ville None 1163 Sep 30  2006 example-demo.py
2: -rw-rw-rw- 1 ville None 1927 Sep 30  2006 example-embed-short.py
3: -rwxrwxrwx 1 ville None 4606 Sep  1 17:15 example-embed.py
4: -rwxrwxrwx 1 ville None 1017 Sep 30  2006 example-gnuplot.py
5: -rwxrwxrwx 1 ville None  339 Jun 11 18:01 extension.py
6: -rwxrwxrwx 1 ville None  113 Dec 20  2006 seteditor.py
7: -rwxrwxrwx 1 ville None  245 Dec 12  2006 seteditor.pyc

Now, let's filter out the 'embed' lines:

[Q:doc/examples]|4> l2 = lines.grep('embed',prune=1)
[Q:doc/examples]|5> l2
                <5> SList (.p, .n, .l, .s, .grep(), .fields() available). Value:

0: total 23
1: -rw-rw-rw- 1 ville None 1163 Sep 30  2006 example-demo.py
2: -rwxrwxrwx 1 ville None 1017 Sep 30  2006 example-gnuplot.py
3: -rwxrwxrwx 1 ville None  339 Jun 11 18:01 extension.py
4: -rwxrwxrwx 1 ville None  113 Dec 20  2006 seteditor.py
5: -rwxrwxrwx 1 ville None  245 Dec 12  2006 seteditor.pyc

Now, we want strings having just file names and permissions:

[Q:doc/examples]|6> l2.fields(8,0)
                <6> SList (.p, .n, .l, .s, .grep(), .fields() available). Value:

0: total
1: example-demo.py -rw-rw-rw-
2: example-gnuplot.py -rwxrwxrwx
3: extension.py -rwxrwxrwx
4: seteditor.py -rwxrwxrwx
5: seteditor.pyc -rwxrwxrwx

Note how the line with 'total' does not raise IndexError.

If you want to split these (yielding lists), call fields() without arguments:

[Q:doc/examples]|7> _.fields()
                <7>
[['total'],
 ['example-demo.py', '-rw-rw-rw-'],
 ['example-gnuplot.py', '-rwxrwxrwx'],
 ['extension.py', '-rwxrwxrwx'],
 ['seteditor.py', '-rwxrwxrwx'],
 ['seteditor.pyc', '-rwxrwxrwx']]

If you want to pass these separated with spaces to a command (typical for lists of files), use the .s property:

[Q:doc/examples]|13> files = l2.fields(8).s
[Q:doc/examples]|14> files
                <14> 'example-demo.py example-gnuplot.py extension.py seteditor.py seteditor.pyc'
[Q:doc/examples]|15> ls $files
example-demo.py  example-gnuplot.py  extension.py  seteditor.py  seteditor.pyc

SList is a subclass of normal python lists, so every list method is available:

[Q:doc/examples]|21> lines.append('hey')

Real world example: remove all files outside version control

First, capture output of "hg status":

[Q:/ipython]|28> out = !hg status
 ==
['M IPython\\Extensions\\ipy_kitcfg.py',
 'M IPython\\Extensions\\ipy_rehashdir.py',
...
 '? build\\lib\\IPython\\Debugger.py',
 '? build\\lib\\IPython\\Extensions\\InterpreterExec.py',
 '? build\\lib\\IPython\\Extensions\\InterpreterPasteInput.py',
...

(lines starting with ? are not under version control).

[Q:/ipython]|35> junk = out.grep(r'^\?').fields(1)
[Q:/ipython]|36> junk
            <36> SList (.p, .n, .l, .s, .grep(), .fields() availab
...
10: build\bdist.win32\winexe\temp\_ctypes.py
11: build\bdist.win32\winexe\temp\_hashlib.py
12: build\bdist.win32\winexe\temp\_socket.py

Now we can just remove these files by doing rm $junk.s .

The .s, .n and .p properties

The '.s' property returns one string where lines are separated by single space (for convenient passing to system commands). The '.n' property return one string where the lines are separated by a '\n' newline (i.e. the original output of the function). If the items in string list are file names, '.p' can be used to get a list of "path" objects for convenient file manipulation.

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