Python refactors

pyrefactors.py

"""
Use setattr
"""

# Normal
item.price = self.request['price']
item.quantity = self.request['quantity']
item.shipping = self.request['shipping']
item.save()

# Pythonic
item_attrs = ['price', 'quantity', 'shipping']
for attr in item_attrs:
    setattr(item, attr, self.request[attr])
item.save()


"""
Use reduce() or list comprehension for incrementing values
"""
# Normal
total_price = 0
for item in items:
    total_price += item.price * item.quantity

# Pythonic
total_price = reduce(lambda x, y: x + y.price * y.quantity, items, 0)
total_price = sum([item.price * item.quantity for item in items])

"""
Use defaultdict() to avoid initializing dictionaries
"""

# Normal
stats = {}

for line in order_lines:
    if line.product_id in stats:
        stats[line.product.id]['quantity'] += line.product.quantity
        stats[line.product.id]['price'] += line.product.price
        stats[line.product.id]['shipping'] += line.product.shipping
    else:
        stats[line.product.id]['quantity'] = 0
        stats[line.product.id]['price'] = 0
        stats[line.product.id]['shipping'] = 0

# Pythonic
from collections import defaultdict

stats = defaultdict(lambda: defaultdict(int))
item_attrs = ['price', 'quantity', 'shipping']

for line in order_lines:
    for attr in item_attrs:
         stats[line.product.id][attr] += getattr(line.product, attr)


"""
Use operator module with reduce()
"""

# Normal
search_keyword = 'iPhone'
Product.objects.filter(
    Q(title__icontains=search_keyword) | Q(description__icontains=search_keyword) | Q(short_title__icontains=search_keyword)
)

# Pythonic
import operator

keys = ['title__icontains', 'description__icontains', 'short_title__icontains']
conditions = [(k, search_keyword) for k in keys]

Product.objects.filter(reduce(operator.or_, [Q(c) for c in conditions]))


"""
Reorganize key-value data pairs
"""
date_dict = {'2003-06-24': 2,
 '2003-08-13': 1,
 '2003-08-19': 2,
 '2003-08-22': 1,
 '2003-08-24': 5}

# Normal
reorganized_date_dict = {'date': date_dict.keys(), 'observations': date_dict.values()}

>>> reorganized_date_dict
{'datetime': ['2003-08-13',
  '2003-08-19',
  '2003-06-24',
  '2003-08-24',
  '2003-08-22'],
 'observations': [1, 2, 2, 5, 1]}

# Using the built-in zip and sorted
dates, observations = zip(*sorted(date_dict.items()))
reorganized_date_dict = {'date': dates, 'observations': observations}

>>> reorganized_date_dict
{'date': ('2003-06-24',
  '2003-08-13',
  '2003-08-19',
  '2003-08-22',
  '2003-08-24'),
 'observations': (2, 1, 2, 1, 5)}