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Mar 27
lots of things about python python
A few interesting things about Python that I had forgotten come from here. I’ve modified the examples.
First, you can use an instance’s namespace to give an interesting way to print strings. Sometimes this will be better: 
# Basic version.
print 'My name is +s and I am +d.' + (p.name, p.age)
# Advanced version.
print 'My name is +(name)s and I am +(age)d.' + p.__dict__
There is also the enumerate function, which returns (index, item) pairs. For example, 
{}{py}
for (index, item) in enumerate(items):
    print index, item
Dictionaries have a setdefault method. Consider these alternative pieces of code: 
# Naive piece of code.
for (cat, amount) in data:
    if cat not in d:
        d[cat] = 0
    d[cat] += amount

# Simpler piece of code.
for (cat, amount) in data:
    d.setdefault(cat, 0)
    d[cat] += amount

# A cunning third option: setdefault also gets.
for (cat, amount) in data:
    d[cat] = d.setdefault(cat, 0) + amount
But, better than all of these optons is the new defaultdict in Python 2.5. 
from collections import defaultdict
d = defaultdict(generator_function)

# Example like those above.
d = defaultdict(lambda: 0)
Finally, generator expressions: say we want to sum a large list that we generate on the fly (ie, we don’t care about the list): 
sum(i**2 for i in xrange(1e5))
(I didn’t find much difference in evaluation time, though.)