我的 Python Cookbook

format(12345, ',') # => 12,345

n [11]: print('The end'.center(20,'+'))
++++++The end+++++++

hello = 'hello '
world = 'world'

hello + world

strs = '%s%s' % (hello, world)

for i in xrange(11):
    print('%02d' % i)

for i in xrange(11):
    print('{0:02d}'.format(i))

s = "\\xe4\\xbd\\xa0\\xe5\\xa5\\xbd"

print(eval("'%s'" % s)) # => 你好

eval("b'%s'" % s).decode("utf-8")  # => 你好

d = {'a': 1, 'b': 2, 'c': 3}
{k:v for k,v in d.items()}      # => {'a': 1, 'c': 3, 'b': 2}

d.items()                       # => [('a', 1), ('c', 3), ('b', 2)

d = {"1": 'a', '2': 'b', '4': 'c', '3': 'd'}
dict(sorted(d.items(), key=lambda i:i[0]))  # => {'1': 'a', '2': 'b', '3': 'd', '4': 'c'}

from collections import defaultdict

d = defaultdict(list)
d['a']                          # 由于键“a”不存在，新建一个键 a，对应的值是空列表
d['b'].append(1)
d                               # defaultdict(list, {'a': [], 'b': [1]})

d = defaultdict(lambda: "hello")
d['a']                          # => 'hello'
d                               # => defaultdict(<function __main__.<lambda>>, {'a': 'hello'})

from collections import Counter

a = {"a": 1, "b": 2, "c": 3}
b = {"c": 3, "b": 1, "e": 100}

merged = Counter(a) + Counter(b)

print(dict(merged))             # => {'a': 1, 'b': 3, 'c': 6, 'e': 10}

l = range(10)

tmp = urls

tmp = urls[:]

for i, value in enumerate(["a", "b", "c"]):
    print(i, value)

[[1, 2], [3, 4], [5]]

[1, 2, 3, 4, 5]

def flatten_list(lst):
    """
    >>> flatten_list([[1, 2], [3, 4], [5]])
    [1, 2, 3, 4, 5]
    """
    def do_flatten():
        for item in lst:
            if hasattr(item, "__iter__") and isinstance(item, list):
                for sub_item in item:
                    yield sub_item
            else:
                yield item

    return list(do_flatten())

from collections import Counter

col = Counter(['a','b','c','a','b','b'])  # => Counter({'b': 3, 'a': 2, 'c': 1})
col["xxx"]                                # => 0，如果访问不存在的值，Counter 不会引发 KeyError 异常，而是返回 0

from collections import defaultdict

count = defaultdict(int)

for i in [1, 2, 3, 4, 5, 5, 3, 1]:
    count[i] += 1

print(count) # => defaultdict(<type 'int'>, {1: 2, 2: 1, 3: 2, 4: 1, 5: 2})

file_ids = ["001", "002", "003", "004", "005", "006", "007"]

step = 3
for i in range(0, len(file_ids), step):
    print(file_ids[i: i + step])

with open('/dev/random', 'rb') as f:
    data = f.read(1024000)
    some_data = data[1024:]

some_data = memoryview(data)[1024:]

some_data[0:10].hex()

urls = ["http://1.com", "http://2.com", "http://3.com"]

while urls:
    url = urls.pop()

    try:
        do_something(url)
    except Exception:
        urls.append(url)
        continue

urls = ["http://1.com", "http://2.com", "http://3.com"]

for url in urls:
    while True:
        try:
            do_something(url)
            break
        except Exception:
            # 出错后反复重试
            continue

self.token = self.login(self.username, self.password)

while True:
    try:
        self.token = self.login(self.username, self.password)
    except requests.exceptions.ConnectionError:
        time.sleep(3)
        continue
    # 如果成功后，就跳出循环
    break

it = (i for i in range(10) if i%2 == 0)
list(it)               # => [0, 2, 4, 6, 8]

sum(i for i in [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] if i%2 == 0)  # => 20

def counter (maximum):
    i = 0
        while i < maximum:
            val = (yield i)
            if val is not None:
                i = val
            else:
                i += 1

it = counter(10)
it.next()                       # => 0
it.next()                       # => 1
it.next()                       # => 2
it.next()                       # => 3
it.send(8)                      # => 8
it.next()                       # => 9

for i in itertools.repeat(1):
    print(i)                    # 无限打印“1”

with open("top-1m.csv") as f:
    for line in f:
        _, domain = line.strip().split(",")

        if domain in data:
            print(domain)

(1,2,3) < (4,5,6)               # True
(1,2,7) < (4,5,6)               # True
(4,2,7) < (4,5,6)               # True

type(name, bases, dict)

c = type("XX", (object, ), {"__init__": lambda: None, "a": 1})
c.a # => 1

import time

for i in xrange(5):
    print i,
    time.sleep(4)

with open('file') as f:
    for c in iter(lambda: f.read(1), ''):
        print(c)

fstream = open('file','r')
fstream.seek(0,os.SEEK_END)    # 将位置移到文件尾
fstream.tell()        # 返回当前位置，就是文件尾。返回的数字就是文件的大小，单位字节

from fileinput import FileInput

with FileInput(files=("/etc/hosts", "/etc/hosts.allow")) as f:
    for line in f:
        print(line)

with open("/path/file") as f:
    data = []

    while True:
        try:
            if len(data) == 3:
                send_to_queue(data)
                data.clear()

            line = next(f).strip()
            data.append(line)
        except StopIteration:
            # 发送余下的数据
            send_to_queue(data)
            break

from os.path import dirname, abspath

print(dirname(abspath(__file__)))

python -m trace --trace script.py

python -m trace --trackcalls script.py

import traceback

def b():
    for func in traceback.extract_stack():
        print(func.name)

def call_b():
    b()

call_b()

try:
    from Queue import Empty
    from Queue import Queue
except ImportError:
    from queue import Empty
    from queue import Queue

if sys.version_info.major == 2:
    # Python2
elif sys.version_info.major == 3:
    # Python3

list(map(print, [1, 2, 3]))
# =>
# 1
# 2
# 3
# [None, None, None]

from __future__ import print_function

print(1, end='')
print(2, end='')