不容错过的Python小贴士—技巧, 风格和最佳实践

a = {}
for i in xrange(0, 1000000):
    a[i] = i
print(type(a))
print(len(a))

def for_func1():
    for x in a:
        pass

def for_func2():
    for x in a.keys():
        pass

def for_func3():
    for x,v in a.iteritems():
        pass

import timeit
print(timeit.timeit(for_func1, number=100))
print(timeit.timeit(for_func2, number=100))
print(timeit.timeit(for_func3, number=100))

students = ('James', 'Andrew', 'Mark')

for i, student in enumerate(students):
    print i, student

students = {'James': 'male', 'Andrew':'male', 'Alice':'female'}

for i, student in enumerate(students):
    print i, student

for ele in ['a', 'b', 'c']:
    if ele == 'b':
        break
else: # no break
    print('for循环完整结束')

for ele in ['a', 'b', 'c']:
    if ele == 'd':
        break
else: # no break
    print('for循环完整结束')

import itertools

#把所有元素放到一个list中
a=[[1],[2],[3,4],[5,6],[7,8,9]]
print list(itertools.chain(*a))

#甚至还能连接不同类型数据dict和list
b=[{'a': 1, 'b': 2},[2],[3,4],[5,6],[7,8,9]]
print list(itertools.chain(*b))

print list(itertools.permutations([1,2,3]))

print list(itertools.combinations([0,1,2,3], 3))

random_numbers = [1,2,3]
names = ('James', 'Andrew', 'Mark')
print zip(random_numbers, names)
d = dict(zip(random_numbers, names))
print d

li=[['a','b','c'],['d','e','f']]
print zip(*li)

dots = [(1, 3), (2, 4), (3, 5)]
print zip(*dots)

with open('/etc/passwd', 'r')as f:
    print f.read()

print(f)

import collections

print collections.Counter(['a', 'b', 'c', 'a', 'b', 'b'])
print collections.Counter({'a':2, 'b':3, 'c':1})
print collections.Counter(a=2, b=3, c=1)

c = collections.Counter()
print 'Initial :', c

c.update('abcdaab')
print 'Sequence:', c

c.update({'a':1, 'd':5})
print 'Dict    :', c

c = collections.Counter()
with open('/usr/share/dict/words', 'rt') as f:
    for line in f:
        c.update(line.rstrip().lower())
print 'Most common:'
for letter, count in c.most_common(3):
    print '%s: %7d' % (letter, count)

from collections import defaultdict

order = (
('Mark', 'Steak'),
('Andrew', 'Veggie Burger'),
('James', 'Steak'),
('Mark', 'Beer'),
('Andrew', 'Beer'),
('James', 'Wine'),
)
#key已经确定, 返回value是list的工厂
group_order = defaultdict(list)

for name, menu_item in order:
    group_order[name].append(menu_item)

print group_order

#key已经确定, 返回value是int的工厂
order_count = defaultdict(int)

for name, menu_item in order:
    order_count[menu_item] += 1

print order_count

from collections import OrderedDict

li_order1=['a','b','c','c']
li_order2=['c','b','a','c']

d1 =  OrderedDict()
d2 = OrderedDict()

for x in li_order1:
    d1[x] = 1
print d1

for x in li_order2:
    d2[x] = 1
print d2

from collections import namedtuple
#namedtuple is a CLASS
Parts = namedtuple('Parts', 'id_num desc cost amount')

auto_parts = Parts(id_num='1234', desc='Ford Engine',
                   cost=1200.00, amount=10)
print auto_parts.id_num

auto_parts = ('1234', 'Ford Engine', 1200.00, 10)
print auto_parts[2]

id_num, desc, cost, amount = auto_parts
print id_num
Parts = {'id_num':'1234', 'desc':'Ford Engine',
                      'cost':1200.00, 'amount':10, 'profit': 10000}
parts = namedtuple('Parts', Parts.keys())(**Parts)
print parts

# define new type
BuildInput = namedtuple('BuildInput', ['name', 'files'])
# test scenarios
b1 = BuildInput('test_build_1', ['file1.txt', 'file2.txt'])

b2 = BuildInput(name='test_build_2', files=['file3.txt', 'file4.txt'])

another_b1 = BuildInput(name='test_build_1', files=['file1.txt', 'file2.txt'])

print b1 != b2
print b1 == another_b1

class Money:
    def __init__(self, dollars, cents):
        self.total_cents = dollars * 100 + cents

    # Getter and setter for dollars...
    @property
    def dollars(self):
        return self.total_cents // 100;
    @dollars.setter
    def dollars(self, new_dollars):
        self.total_cents = 100 * new_dollars + self.cents

    # And the getter and setter for cents.
    @property
    def cents(self):
        return self.total_cents % 100;
    @cents.setter
    def cents(self, new_cents):
        self.total_cents = 100 * self.dollars + new_cents

# with the final Money class. High five!
money = Money(27, 12)
message = "I have {:d} dollars and {:d} cents."
print(message.format(money.dollars, money.cents))
# "I have 27 dollars and 12 cents."

money.dollars += 2
money.cents += 20
print(message.format(money.dollars, money.cents))
# "I have 29 dollars and 32 cents."

# This works correctly, too.
money.cents += 112
print(message.format(money.dollars, money.cents))
# "I have 30 dollars and 44 cents."

a = (x**2 for x in [1,2,3,4,5])

print(type(a))
for i in a:
    print(i)

b = [x**2 for x in [1,2,3,4,5]]
print(b)