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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]
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 http://www.wellho.net/resources/ex.php4?item=y111/sal 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"), \ ("Christmas",20052512,"Worldwide")] # Sort events by date events = [(a[1],a[0],a[2]) for a in events] events.sort() 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
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* Learning to program in Python * Python Programming * Intermediate Python Also available on on site courses for larger groups Books covering this topic
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