Averroes

=== Keeping the Last N Items

==== Problem

You want to keep a limited history of the last few items seen
during iteration or during some other kind of processing.

==== Solution

Keeping a limited history is a perfect use for a `collections.deque`.

Averroes

# example.py

from collections import namedtuple

Stock = namedtuple('Stock', ['name', 'shares', 'price'])

def compute_cost(records):
    total = 0.0
    for rec in records:
        s = Stock(*rec)

Averroes

# example.py
#
# Remove duplicate entries from a sequence while keeping order

def dedupe(items):
    seen = set()
    for item in items:
        if item not in seen:
            yield item
            seen.add(item)

Averroes

# example2.py
#
# Remove duplicate entries from a sequence while keeping order

def dedupe(items, key=None):
    seen = set()
    for item in items:
        val = item if key is None else key(item)
        if val not in seen:
            yield item

Averroes

# example.py
#
# Sort a list of a dicts on a common key

rows = [
    {'fname': 'Brian', 'lname': 'Jones', 'uid': 1003},
    {'fname': 'David', 'lname': 'Beazley', 'uid': 1002},
    {'fname': 'John', 'lname': 'Cleese', 'uid': 1001},
    {'fname': 'Big', 'lname': 'Jones', 'uid': 1004}
]

Averroes

from operator import attrgetter

class User:
    def __init__(self, user_id):
        self.user_id = user_id
    def __repr__(self):
        return 'User({})'.format(self.user_id)

# Example
users = [User(23), User(3), User(99)]

Averroes

# example.py
#
# Some examples of using generators in arguments

import os
files = os.listdir(os.path.expanduser('~'))
if any(name.endswith('.py') for name in files):
    print('There be python!')
else:
    print('Sorry, no python.')

Averroes

# example.py
#
# Unpacking of tagged tuples of varying sizes

records = [
     ('foo', 1, 2),
     ('bar', 'hello'),
     ('foo', 3, 4),
]

Averroes

# example.py
#
# Example of combining dicts into a chainmap

a = {'x': 1, 'z': 3 }
b = {'y': 2, 'z': 4 }

# (a) Simple example of combining
from collections import ChainMap
c = ChainMap(a,b)

Averroes

import sys
sys.path.extend(['foo-package', 'bar-package'])
import spam.blah
import spam.grok