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Python equivalent of Schwartzian transform
More on Collections and Sequences example from a Well House Consultants training course
More on More on Collections and Sequences [link]

This example is described in the following article(s):
   • Snippets from Geekmas - [link]

This example references the following resources:

Source code: dsd Module: Y111

""" Requirement - to sort objects in a way which is
not their natural sort order. You *could* do it by
passing in the name of a comparator method to sort - see
but in such a case each element to be sorted is manipulated
multiple times in order to extract the element on which
the comparision is to be made.

By transforming the whole of the incoming list once into
a form in which the natural sort order does the job, then
sorting, then transforming back, you can do the job neatly
and efficiently, and without the need for a callback.

If we were using Perl rather than Python, the idiom of the
Schwartzian transform is used in this way, although there
the idiom is to write just a single nested line. This Perl
approach makes the whole thing hard to read / debug for a
newcomer; the Python approach (below) is much more readable"""

events = [("Geekmas",20051127,"404, The Spa"), \
        ("Public Python Course",20060109,"404, The Spa"), \
        ("New Year",20060101,"Worldwide"), \
        ("Manor Opening",20060601,"Spa Road, Melksham"), \

# Sort events by date

events = [(a[1],a[0],a[2]) for a in events]
events = [(a[1],a[0],a[2]) for a in events]

# Could use following line instead to do transform
# events = map(lambda a:(a[1],a[0],a[2]), events)

print events
Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in Python
 * Python Programming
 * Intermediate Python
Also available on on site courses for larger groups

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Other Examples
This example comes from our "More on Collections and Sequences" training module. You'll find a description of the topic and some other closely related examples on the "More on Collections and Sequences" module index page.

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