My rule to see if a framework is worth of attention

I came up with a little rule:

In order to be worth of any attention, a framework must be stable enough that I can charge money to train people to use it.

This probably applies to other kinds of software stacks, libraries, development environments and, well, to most software applications.

In the context of python web frameworks, this means that:

• If it changes API all the time it is not worth of attention, because my customers won't get value for their money, as they'd continuously need retraining and rewriting their software.
• If I see lots of DeprecationWarnings it is not worth of attention, because my customers will see them and blame me for teaching them deprecated stuff.
• If fixes for bugs affecting the stable version are only distributed "in a recent git" or "in the next development version", and they are not backported into a new bugfix-only stable release, then it is not worth of attention, because:
  • my customers' business is to develop their own products based on the framework.
  • My customers' business is not to be maintaning in-house stable updates of the framework. Although if the framework's community is nice enough they might end up giving a hand.
• If it requires virtualenv or can only be obtained through easy_install it is not worth of attention, because:
  • my customers are not interested in maintaning custom deployment environments over time.
  • My customers are not interested in tracking each and every single library's upstream development to keep their production system free of bugs.
  • My customers are used to getting software through a proper distribution which also takes care of security updates.
  • I am paid to teach them how to use a framework, not a custom python-only package management system.
  • In my experience, if distributions have trouble keeping packages up to date, upstream is doing something fundamentally wrong.

In light of this rule, I regret to notice that I see very few python web frameworks worth of any attention.

On python stable APIs

There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.

There is another theory which states that this has already happened.

In Debian testing:

/usr/lib/python2.6/dist-packages/sqlalchemy/types.py:547: SADeprecationWarning: The Binary type has been renamed to LargeBinary.

In Debian Lenny:

ImportError: cannot import name LargeBinary

I was starting to think that SQLAlchemy wasn't too bad, since I've been using it for 6 months and I haven't seen its API change yet.

But there it is, a beautiful reminder that SQLAlchemy, too, is part of the marvelously autistic Python ecosystem.

Released cfget 0.16

I have released version 0.16 of cfget.

It is just a little bugfix release as I found a bug in the new expression parser, and while I was at it I simplified its code quite a bit.

On python, frameworks and TOOWTDI

The Python world is ridden with frameworks, microframeworks, metaframeworks and their likes. They are often very clever things, but more often than not they are a tool of despair.

A very peculiar thing about Python web frameworkish things is that there are so many of them. There's cherrypy (in its various API redesigns), fapws, gunicorn, bottle and flask, paste, werkzeug and flup, tornado, pylons, turbogears 1 and 2, django, repoze who, what and whatnot, all the myriad of rendering engines and buffet as a metathing on top of them, diesel, twisted, and I apologise if I don't spend my day listing and hyperlinking them all, I hope I made my point.

Frameworks are supposed to standardise some aspects of programming; the nice thing about standards is that there are so many of them to choose from, and they all suck, so I'll make my own.

But wasn't Python supposed to be the world of TIOOWTDI?

Ok, everbody knows it isn't. Just in the standard library there are 2 implementations of pickle and 2 urllibs. But people like the TIOOWTDI idea.

I believe the reason people like the TIOOWTDI idea is because it creates a framework. It standardises some aspects of programming, and defines building blocks that guarantee that people doing similar jobs will be using similar sets of components.

Let's take for example the datetime module in the standard library. It is an embarassing example of a badly designed module, so embarassing that the standard library documentation continuously fails to document its fundamental design flaws and common work-arounds hoping that noone notices them, but as a consequence each poor soul starting to use it for nontrivial things has to google for hours in despair to rediscover in how many ways it's broken.

But still, datetime works as a structure to hold those values that make a date, time, or full UTC timestamp. For that job it's become the standard, and as such it's an important component of the Python TIOOWTDI framework: one can use it to exchange datetimes among different libraries: for example ORMs are using it instead of rolling their own, which makes database programming so much easier when date/time is involved.

Even if the implementation is far from perfect, once we apply TIOOWTDI to dates and timestamps, python code from different authors can exchange dates without worries. This is much better than having 3 different superior datetime libraries and having to convert date objects from one to another when passing values from a web form to an ORM.

There is an often overlooked Python framework. The Pyton framework. It's called TIOOWTDI.

All the micro-mini-midi-maxi-meta-frameworks that people scatter around, are, or should be, just experiments, proofs of concept, competing ideas waiting to be distilled in The Only One Way, bringing the Python experience one step forward.

What is unfortunate is that this last distillation thing happens so rarely that people get used to the idea of having to use proof of concept code to get things done.

Update:

this post apparently wasn't very clear, so here is some clarification:

• that python, plus the idea of TIOOWTDI, in fact generate a framework, the framework;
• that framework currently includes very little web stuff;
• the web stuff is currently shipped in countless prototypes and proof of concept things;
• something from all the prototypes people develop ought to be brought into the TIOOWTDI "framework";
• otherwise people get used (or worse, forced) to use proof of concept throwaway code to get their job done.

Released cfget 0.15

I have released version 0.15 of cfget.

cfget is a tool to extract values from ini-style config files. A trivial thing, really.

It is also simple to install: it is a single python executable and it has no dependencies besides the python standard library.

It is trivial and simple, but because of the complex requirements (and sponsorship) of ISAC - CNR it has recently accumulated quite a set of features, and it manages to get a remarkable lot of things done.

There are several news since 0.8, worth a rather major announcement:

Added --dump=pickle

Now all the contents of the configuration files, plus all the contents generated by cfget plugins, can be dumped in pickle format.

This provides a quick and dirty way to load all cfget-generated data into a python dict:

data = pickle.loads(
    subprocess.Popen(
        ["cfget", "--dump=pickle"],
        stdout=subprocess.PIPE).communicate()[0])

It sounds like a rather complicated way to read a configuration file, but if you have various plugins that compute nontrivial derived configuration values, that quick&dirty hack could be quite useful.

Curly brace expansion

Suppose that you have a config file like this:

[general]
mode = show

[show]
command = display

[edit]
command = gimp

And you want to get the command from the section indicated by general/mode.

Now you can, very easily: cfget '{general/mode}/command'

When it notices curly braces, cfget will literally replace them with the result of querying their contents, then parse the expression again.

Simple expression support

ISAC - CNR are using cfget to configure the run of a rather complicated physical model, and use plugins to derive all sorts of values form the base configuration.

This works, but there are times when adding a function to a plugin sounds like overkill: for example, sometimes one needs foo/bar + 1, or just the hour of a timestamp.

For those simple cases, I've added support for simple expressions:

• operators: +, -, *, /, **
• grouping with parentesis
• function calls (int(), round()), with the possibility to define new functions via plugins.

So to compute a middle point one can now do this:

cfget "round((pos/start + pos/end) / 2)"

It needs a space around arithmetic operators to avoid conflicts with characters used to refer to configuration values, but with the space the expressions look nicer, so the result is that it generally does the right thing.

Just as a scary thought, curly braces work with and in expressions:

cfget "values/val{round((pos/end - pos/start) / 2)} + 1"

Although if someone ends up having a hairy thing like that, it is worth considering to replace it with a dynamic value computed using a plugin.

Computing time offsets between EXIF and GPS

I like the idea of matching photos to GPS traces. In Debian there is gpscorrelate but it's almost unusable to me because of bug #473362 and it has an awkward way of specifying time offsets.

Here at SoTM10 someone told me that exiftool gained -geosync and -geotag options. So it's just a matter of creating a little tool that shows a photo and asks you to type the GPS time you see in it.

Apparently there are no bindings or GIR files for gtkimageview in Debian, so I'll have to use C.

Here is a C prototype:

/*
 * gpsoffset - Compute EXIF time offset from a photo of a gps display
 *
 * Use with exiftool -geosync=... -geotag trace.gpx DIR
 *
 * Copyright (C) 2009--2010  Enrico Zini <enrico@enricozini.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */


#define _XOPEN_SOURCE /* glibc2 needs this */
#include <time.h>
#include <gtkimageview/gtkimageview.h>
#include <libexif/exif-data.h>
#include <stdio.h>
#include <stdlib.h>

static int load_time(const char* fname, struct tm* tm)
{
    ExifData* exif_data = exif_data_new_from_file(fname);
    ExifEntry* exif_time = exif_data_get_entry(exif_data, EXIF_TAG_DATE_TIME);
    if (exif_time == NULL)
    {
        fprintf(stderr, "Cannot find EXIF timetamp\n");
        return -1;
    }

    char buf[1024];
    exif_entry_get_value(exif_time, buf, 1024);
    //printf("val2: %s\n", exif_entry_get_value(t2, buf, 1024));

    if (strptime(buf, "%Y:%m:%d %H:%M:%S", tm) == NULL)
    {
        fprintf(stderr, "Cannot match EXIF timetamp\n");
        return -1;
    }

    return 0;
}

static time_t exif_ts;
static GtkWidget* res_lbl;

void date_entry_changed(GtkEditable *editable, gpointer user_data)
{
    const gchar* text = gtk_entry_get_text(GTK_ENTRY(editable));
    struct tm parsed;
    if (strptime(text, "%Y-%m-%d %H:%M:%S", &parsed) == NULL)
    {
        gtk_label_set_text(GTK_LABEL(res_lbl), "Please enter a date as YYYY-MM-DD HH:MM:SS");
    } else {
        time_t img_ts = mktime(&parsed);
        int c;
        int res;
        if (exif_ts < img_ts)
        {
            c = '+';
            res = img_ts - exif_ts;
        }
        else
        {
            c = '-';
            res = exif_ts - img_ts;
        }
        char buf[1024];
        if (res > 3600)
            snprintf(buf, 1024, "Result: %c%ds -geosync=%c%d:%02d:%02d",
                    c, res, c, res / 3600, (res / 60) % 60, res % 60);
        else if (res > 60)
            snprintf(buf, 1024, "Result: %c%ds -geosync=%c%02d:%02d",
                    c, res, c, (res / 60) % 60, res % 60);
        else
            snprintf(buf, 1024, "Result: %c%ds -geosync=%c%d",
                    c, res, c, res);
        gtk_label_set_text(GTK_LABEL(res_lbl), buf);
    }
}

int main (int argc, char *argv[])
{
    // Work in UTC to avoid mktime applying DST or timezones
    setenv("TZ", "UTC");

    const char* filename = "/home/enrico/web-eddie/galleries/2010/04-05-Uppermill/P1080932.jpg";

    gtk_init (&argc, &argv);

    struct tm exif_time;
    if (load_time(filename, &exif_time) != 0)
        return 1;

    printf("EXIF time: %s\n", asctime(&exif_time));
    exif_ts = mktime(&exif_time);

    GtkWidget* window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    GtkWidget* vb = gtk_vbox_new(FALSE, 0);
    GtkWidget* hb = gtk_hbox_new(FALSE, 0);
    GtkWidget* lbl = gtk_label_new("Timestamp:");
    GtkWidget* exif_lbl;
    {
        char buf[1024];
        strftime(buf, 1024, "EXIF time: %Y-%m-%d %H:%M:%S", &exif_time);
        exif_lbl = gtk_label_new(buf);
    }
    GtkWidget* date_ent = gtk_entry_new();
    res_lbl = gtk_label_new("Result:");
    GtkWidget* view = gtk_image_view_new();
    GdkPixbuf* pixbuf = gdk_pixbuf_new_from_file(filename, NULL);

    gtk_box_pack_start(GTK_BOX(hb), lbl, FALSE, TRUE, 0);
    gtk_box_pack_start(GTK_BOX(hb), date_ent, TRUE, TRUE, 0);

    gtk_signal_connect(GTK_OBJECT(date_ent), "changed", (GCallback)date_entry_changed, NULL);
    {
        char buf[1024];
        strftime(buf, 1024, "%Y-%m-%d %H:%M:%S", &exif_time);
        gtk_entry_set_text(GTK_ENTRY(date_ent), buf);
    }

    gtk_widget_set_size_request(view, 500, 400);
    gtk_image_view_set_pixbuf(GTK_IMAGE_VIEW(view), pixbuf, TRUE);
    gtk_container_add(GTK_CONTAINER(window), vb);
    gtk_box_pack_start(GTK_BOX(vb), view, TRUE, TRUE, 0);
    gtk_box_pack_start(GTK_BOX(vb), hb, FALSE, TRUE, 0);
    gtk_box_pack_start(GTK_BOX(vb), exif_lbl, FALSE, TRUE, 0);
    gtk_box_pack_start(GTK_BOX(vb), res_lbl, FALSE, TRUE, 0);
    gtk_widget_show_all(window);

    gtk_main ();

    return 0;
}

And here is its simple makefile:

CFLAGS=$(shell pkg-config --cflags gtkimageview libexif)
LDFLAGS=$(shell pkg-config --libs gtkimageview libexif)

gpsoffset: gpsoffset.c

It's a simple prototype but it's a working prototype and seems to do the job for me.

I currently cannot find out why after I click on the text box, there seems to be no way to give the focus back to the image viewer so I can control it with keys.

There is another nice algorithm to compute time offsets to be implemented: you choose a photo taken from a known place and drag it on that place on a map: you can then look for the nearest point on your GPX trace and compute the time offset from that.

I have seen that there are programs for geotagging photos that implement all such algorithms, and have a nice UI, but I haven't seen any in Debian.

Are there any such softwares that can be packaged?

If not, the interpolation and annotation tasks can now already be performed by exiftool, so it's just a matter of building a good UI, and I would love to see someone picking up the task.

Searching OSM nodes in Spatialite

Third step of my SoTM10 pet project: finding the POIs.

I put together a query to find all nodes with a given tag inside a bounding box, and also a query to find all the tag values for a given tag name inside a bounding box.

The result is this simple POI search engine:

#
# poisearch - simple geographical POI search engine
#
# Copyright (C) 2010  Enrico Zini <enrico@enricozini.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#

from pysqlite2 import dbapi2 as sqlite

class PoiDB(object):
    def __init__(self):
        self.db = sqlite.connect("pois.db")
        self.db.enable_load_extension(True)
        self.db.execute("SELECT load_extension('libspatialite.so')")
        self.oldsearch = []
        self.bbox = None

    def set_bbox(self, xmin, xmax, ymin, ymax):
        '''Set bbox for searches'''
        self.bbox = (xmin, xmax, ymin, ymax)

    def tagid(self, name, val):
        '''Get the database ID for a tag'''
        c = self.db.cursor()
        c.execute("SELECT id FROM tag WHERE name=? AND value=?", (name, val))
        res = None
        for row in c:
            res = row[0]
        return res

    def tagnames(self):
        '''Get all tag names'''
        c = self.db.cursor()
        c.execute("SELECT DISTINCT name FROM tag ORDER BY name")
        for row in c:
            yield row[0]

    def tagvalues(self, name, use_bbox=False):
        '''
        Get all tag values for a given tag name,
        optionally in the current bounding box
        '''
        c = self.db.cursor()
        if self.bbox is None or not use_bbox:
            c.execute("SELECT DISTINCT value FROM tag WHERE name=? ORDER BY value", (name,))
        else:
            c.execute("SELECT DISTINCT tag.value FROM poi, poitag, tag"
                      " WHERE poi.rowid IN (SELECT pkid FROM idx_poi_geom WHERE ("
                      "       xmin >= ? AND xmax <= ? AND ymin >= ? AND ymax <= ?) )"
                      "   AND poitag.tag = tag.id AND poitag.poi = poi.id"
                      "   AND tag.name=?",
                      self.bbox + (name,))
        for row in c:
            yield row[0]

    def search(self, name, val):
        '''Get all name:val tags in the current bounding box'''
        # First resolve the tagid
        tagid = self.tagid(name, val)
        if tagid is None: return

        c = self.db.cursor()
        c.execute("SELECT poi.name, poi.data, X(poi.geom), Y(poi.geom) FROM poi, poitag"
                  " WHERE poi.rowid IN (SELECT pkid FROM idx_poi_geom WHERE ("
                  "       xmin >= ? AND xmax <= ? AND ymin >= ? AND ymax <= ?) )"
                  "   AND poitag.tag = ? AND poitag.poi = poi.id",
                  self.bbox + (tagid,))
        self.oldsearch = []
        for row in c:
            self.oldsearch.append(row)
            yield row[0], simplejson.loads(row[1]), row[2], row[3]

    def count(self, name, val):
        '''Count all name:val tags in the current bounding box'''
        # First resolve the tagid
        tagid = self.tagid(name, val)
        if tagid is None: return

        c = self.db.cursor()
        c.execute("SELECT COUNT(*) FROM poi, poitag"
                  " WHERE poi.rowid IN (SELECT pkid FROM idx_poi_geom WHERE ("
                  "       xmin >= ? AND xmax <= ? AND ymin >= ? AND ymax <= ?) )"
                  "   AND poitag.tag = ? AND poitag.poi = poi.id",
                  self.bbox + (tagid,))
        for row in c:
            return row[0]

    def replay(self):
        for row in self.oldsearch:
            yield row[0], simplejson.loads(row[1]), row[2], row[3]

Problem 3 solved: now on to the next step, building a user interface for it.