Learning Python via a little word frequency program

Andrew Savige ajsavige at yahoo.com.au
Wed Jan 9 11:58:20 CET 2008


I'm learning Python by reading David Beazley's "Python Essential Reference"
book and writing a few toy programs. To get a feel for hashes and sorting,
I set myself this little problem today (not homework, BTW):

  Given a string containing a space-separated list of names:

    names = "freddy fred bill jock kevin andrew kevin kevin jock"

  produce a frequency table of names, sorted descending by frequency.
  then ascending by name. For the above data, the output should be:

    kevin     : 3
    jock      : 2
    andrew    : 1
    bill      : 1
    fred      : 1
    freddy    : 1

Here's my first attempt:

names = "freddy fred bill jock kevin andrew kevin kevin jock"
freq = {}
for name in names.split():
    freq[name] = 1 + freq.get(name, 0)
deco = zip([-x for x in freq.values()], freq.keys())
deco.sort()
for v, k in deco:
    print "%-10s: %d" % (k, -v)

I'm interested to learn how more experienced Python folks would solve
this little problem. Though I've read about the DSU Python sorting idiom,
I'm not sure I've strictly applied it above ... and the -x hack above to
achieve a descending sort feels a bit odd to me, though I couldn't think
of a better way to do it.

I also have a few specific questions. Instead of:

for name in names.split():
    freq[name] = 1 + freq.get(name, 0)

I might try:

for name in names.split():
    try:
        freq[name] += 1
    except KeyError:
        freq[name] = 1

Which is preferred?

Ditto for:

deco = zip([-x for x in freq.values()], freq.keys())

versus:

deco = zip(map(operator.neg, freq.values()), freq.keys())

Finally, I might replace:

for v, k in deco:
    print "%-10s: %d" % (k, -v)

with:

print "\n".join("%-10s: %d" % (k, -v) for v, k in deco)

Any feedback on good Python style, performance tips, good books
to read, etc. is appreciated.

Thanks,
/-\


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