分享Python 的十个小技巧
一. 列表、字典、集合、元组的使用
from random import randint, sample
# 列表解析
data = [randint(-10, 10) for _ in xrange(10)]
filter(lambda x: x >= 0, data)
[x for x in data if x >= 0] #最快速
# 字典解析
d = {x: randint(60, 100) for x in xrange(1,21)}
{k : v for k, v in d.iteritems() if v > 90}
# 集合解析
s = set(data)
{x for x in s if x % 3 ==0}
# 元组
student = ('Jim', 16, 'male', 'jim@qq.com')
# 1. enum
NAME, AGE, SEX, EMaiL = xrange(4)
print student[NAME]
# 2.
from collections import namedtuple
Student = namedtuuple('Student', ['name', 'age', 'sex', 'email'])
s2 = Student('Tom', 16, 'mail', 'tom@qq.com')
print s2.name
# 统计列表的重复元素
li = [randint(0, 20) for _ in xrange(30)]
d = dict.fromkeys(li, 0)
# 1.
for x in li: d[x] += 1
# 2.
from collections import Counter
d2 = Counter(li)
d2.most_common(3) #重复数最高的三个元素
# 字典根据值value排序
sorted([3, 1, 5]) #排序列表
(97, 'a') > (88, 'b') # 元组的比较，每个元素从开始比较
d = {x: randint(60, 100) for x in 'abcde'}
# 1.
data = zip(d.itervalues(), d.iterkeys())
sorted(data)
# 2.
sorted(d.items(), key=lambda x: x[1])
# 多个字典中的公共键
sample('abcdefg', 3)
sample('abcdefg', randint(3,6)) # 随机取出几个元素
s1 = {x: randint(1,4) for x in sample('abcdefg', randint(3.6))}
s2 = {x: randint(1,4) for x in sample('abcdefg', randint(3.6))}
s3 = {x: randint(1,4) for x in sample('abcdefg', randint(3.6))}
# 1.
res = []
for k in s1: if k in s2 and k in s3: res.append(k) # res.pop(k)
# 2. 使用集合
res = s1.viewkeys() & s2.viewkeys() & s3.viewkeys()
# 3.
m1 = map(dict.viewkeys, [s1, s2, s3])
res = reduce(lambda a, b: a & b, m1)
# 保持字典有序
d = {'Jim':(1, 35), 'Leo':(2, 38), 'Tom':(3, 44)}
from collections import OrderedDict
d = OrderedDict() #按进入字典的顺序打印
d['Jim'] = (1,35)
d['Leo'] = (2,38)
d['Tom'] = (3,44)
from time import time
start = time()
raw_input() #等待输入
# ...
timesecond = time() - start
# 历史记录
# 1. 用队列存储
from collections import deque
q = deque([], 5)
q.append(1) # 达到长度后，先进先出
li = list(q) # 转换成列表类型
# 2. 将q存到文件中
import pickle
pickle.dump(q, open('test','w'))
q2 = pickle.load(open('test','r'))
二. 迭代器、生成器
# 实现可迭代对象、迭代器对象
# 用时访问 并封装到一个对象中
# 可迭代对象
li = [1,2,3,4]
str= 'abcde'
# 迭代器
iterl = iter(li) # li.__iter__()
iters = iter(str) # str.__getitem__()
iterl.next()
# 1. 城市天气的迭代器和可迭代对象
from collections import Iterable, Iterator
class WIterator(Iterator):
def __init__(self, cities):
self.cities = cities
self.index = 0
def getWeather(city):
import requests
r = requests.get(u'Http://wthrcdn.etouch.cn/weather_mini?city=' + city)
data = r.JSON()['data']['forecast'][0]
return '%s: %s, %s' % (city, data['low'], data['high'])
def next(self):
if self.index == len(self.cities)
raise StopIteration
city = self.cities[self.index]
self.index += 1
return self.getWeather(city)
class WIterable(Iterable):
def __init__(self, cities):
self.cities = cities
def __iter__(self):
return WIterator(self.cities)
for x in WIterable([u'北京', u'长沙', u'广州'])：
print x
# 2. 使用生成器函数实现可迭代对象
def f():
print 'in f(), 1'
yield 1
print 'in f(), 2'
yield 2
g = f() # g.__iter__()
for i in g: print i
class PrintNumbers:
def __init__(self, start, end):
self.start = start
self.end = end
def isPrimeNum(self, k):
if k % 2 == 0:
return True
else:
return False
def __iter__(self):
for k in xrange(self.start, self.end+1):
if self.isPrimeNum(k):
yield k
for x in PrintNumbers(1, 100): print x
# 进行反向迭代
li = [1,2,3,4,5]
li.reverse() # 改变原来列表
li[::-1] # 切片，和原来列表等大的新列表
ll = li.reversed(li) # 列表反向迭代
for i in ll: print i
class FloatRange:
def __init__(self, start, end, step=0.1)
self.start = start
self.end = end
self.step = step
def __iter__(self):
t = self.start
while t <= self.end:
yield t
t += self.step
def __reversed__(self):
t = self.enf
while t >= self.start:
yield t
t -= self.step
# 正向迭代
for i in FloatRange(1.0, 4.0, 0.5): print x
# 反向迭代
for i in reversed(FloatRange(1.0, 4.0, 0.5)): print x
# 对迭代器做切片操作
from itertools import islice
# islice()
li = range(20)
t = iter(li)
for x in islice(t, 5, 10): print x # 会消耗原来的迭代对象
# 在一个for中迭代多个可迭代对象
chinese = [randint(60,100) for _ in xrange(40)]
math = [randint(60,100) for _ in xrange(40)]
english = [randint(60,100) for _ in xrange(40)]
for in in xrange(len(math)):
print chinese[i] + math[i] + english[i]
total = []
# 并行多个可迭代对象
for c, m, e in zip(chiness, math, english)
print c+m+e
# 1. 串连多个迭代对象
from itertools import chain
c1 = [randint(60,100) for _ in xrange(40)]
c2 = [randint(60,100) for _ in xrange(42)]
c3 = [randint(60,100) for _ in xrange(45)]
for s in chain(c1, c2, c3):
if s > 90: print s
三. 字符串
# 拆分含多种分隔符的字符串
s = "fwerf sd123 ^sdf dfdsf*d dsf 123"
s.split(“xy”) #默认以空格分割，或以参数分割
res = s.split(";")
map(lambda x: x.split("|"), res) # 以";"和"|"分割的二维数组
t = []
map(lambda x: t.extend(x.split("|")), res) # 二维元素放到t中
# 1.
def aSplit(s, ds):
res = [s]
for d in ds:
t = []
map(lambda x: t.extend(x.split(d)), res)
res = t
return res
print aSplit(s, " ^*") # 会存在空的元素
# 2. 正则表达式
import re
re.split(r'[,;|]+', s)
# 判断字符串a是否以b开头或结尾
#s.startswith() s.endswith() 接收单个字符串或字符串元组
import os, stat
files = [name for name in os.listdir(".") if name.endswith(('.sh', '.py'))]
# 调整字符串中文本的格式
#日志中'yyyy-mm-dd' 改为 'mm/dd/yyyy'
import re
log = open("/var/log/dpkg.log").read()
re.sub('(\d{4})-(\d{2})-(\d{2})', r'\2/\3/\1', log)
re.sub('(?P\d{4})-(?P\d{2})-(?P\d{2})', r'\g/\g/\g', log)
# 多个小字符串拼接成大字符串
s1 = "abcde"
s2 = "12345"
s1 + s2 # str.__add__(s1, s2) str.__gt__(s1, s2) 运算符重载
s = ""
for p in pl: s += p # 变量多时，临时变量开销大，资源浪费
s.join(s1) # 参数可为字符串，可为列表
li = ['avc', 123, 'xyz', 456]
''.join([str(x) for x in li]) #列表解析，会生成一个列表，开销大
''.join(str(x) for x in li) #生成器, (str(x) for x in li) 作为参数是括号省略
# 字符串格式对齐
# str.ljust() str.rjust() str.center()
s = "abc"
s.ljust(10 ,'=') # 左对齐，填充=
s.center(10)
fORMat(s, '<20') # 左对齐
format(s, '>20') # 右对齐
format(s, '^20') # 居中
# 去掉字符串中不需要的字符
s = ' -------sd dfadf 2332 +++++++++'
s.strip(' -+')
s.lstrip()
s.rstirp()
# 删除固定位置的字符,拼接切片
s[:3]+ s[4:]
# 替换
s.replace('\t', '')
import re
re.sub('[\t\r]', '', s)
s = 'abc123e3rxyz'
#s.translate()
import string
tr = string.maketrans('abcxyz', 'xyzabc')
s.translate(tr)
s = 'abc\rdfd\n234234\t'
s.translate(None, '\r\t\n')
四. 文件读写
# python2 str unicode
# python3 bytes str
# Python2
s = u'你好'
s.encode('utf8') #存储到文件中的格式
f = open('hello.txt', 'w')
f.write(s.encode('utf8'))
f.close()
f = open('hello.txt', 'r')
t = f.read().decode('utf8') # 你好
f.close()
# python3 字符串就是unicode
strb = b'asdfasdfsdg'
s = '你好'
f = open('hello2.txt', 'wt', encoding='utf8') # 自动完成编解码
f.write(s)
f.close()
f = open('hello2.txt', 'rt', encoding='utf8')
s = f.read()
f.close()
# 处理二进制文件 处理音频文件，将音量调小保存
f = open('demo.wav', 'rb')
info = f.read(44) #文件头
import struct
struct.unpack('h',info[22:24]) #处理文件头 数据运算
struct.unpack('i',infi[24:28])
f.seek(0,2)
f.tell()
n = (f.tell()-44) /2
import array
buf = array.array('h', (0 for _ in xrange(n)))
f.seek(44)
f.readinto(buf)
for i in xrange(n): buf[i] /= 8
f2 = open('demo2.wav', 'wb')
f2.write(info)
buf.tofile(f2)
f2.close()
# 使用临时文件
# 自动删除，不占内存
from tempfile import TemporaryFile, NamedTemporaryFile
f = TemporaryFile() # 系统文件系统找不到
f.write('abcddee'*100000)
f.seek(0)
f.read(100)
ntf = NamedTemporaryFile(delete=False) # 能找到文件，默认关闭以后会删除文件
fname = nft.name
# 设置文件的缓冲
# I/O 操作以块为单位，如4096字节一个块
f = open('test.txt', 'w'， buffering=2048) # 全缓冲，要写满缓冲才会写到文件中
f = open('test.txt', 'w'， buffering=1) # 行缓冲，\n就会写文件
f = open('test.txt', 'w'， buffering=1) # 无缓冲，实时写
f.write('abc')
# 将文件映射到内存
import mmap
f = open('demo.bn','r+b')
f.fileno()
m = mmap.mmap(f.fileno(), 0, access=mmpa.ACCESS_WRITE, offset=mmap.PAGESIZE)
# 得到字节数组
m[4:8] = '\xff'*4 # 修改直接改变文件内容
# 读写csv数据
from urllib import urlretrieve
urlretrieve('http://table.finance.yahoo.com/table.csv?s=000001.sz', 'pingan.csv')
rf = open('pingan.csv', 'rb')
import csv
reader = csv.reader(rf)
header = reader.next()
wf = open('pingan_c.csv', 'wb')
writer = csv.writeer(wf)
writer.writerow(header)
rf.close()
wf.close()
# 读写json数据
import requests
import json
from record import Record
record = Record(channel=1)
audioData = record.record(2)
from secret import api_KEY, SECRET_KEY
authUrl = "https://openapi.baidu.com/oauth/2.0/token?grant_type=client_credentials&client_id=" + API_KEY + "&client_secret=" + SECRET_KEY
response = requests.get(authUrl)
res = json.loads(response.content)
token = res['access_token']
#百度语音识别
cuid = 'xxxxxxxxxxxxx'
srvUrl = 'http://vop.baidu.com/server_api?cuid=' + cuid + '&token=' + token
heepHeader = {'Content-Type': 'audio/wav; rate = 8000'}
response = requests.post(srvUrl, headers=httpHeader, data=audioData)
res = json.loads(response.content)
text = res['result'][0]
print text
# json.dumps() python对象(列表、字典等)转换成json字符串
# json.dumps(data, sort_keys=True)
# json.loads() json字符串转换成python对象
with open('demo.json', 'wb') as f:
json.dump(l, f) # 将l数据写到文件
# 构建xml文档
from xml.etree.ElementTree import parse
with open('demo.xml') with f:
et = parse(f)
root = et.getroot()
root.tag
root.attrib
root.text
#root.getchildren()
for child in root:
print child.get('name')
root.find('country')
root.findall('country') # 直接子元素
for e in root.iterfind('country'):
print e.get('name')
from xml.etree.ElementTree import Element, ElementTree, tostring
e = Element('Data')
e.set('name', 'abc')
e2 = Element('Row')
e3 = Element('Open')
e3.text = '8.80'
e2.append(e3)
e.append(e2)
tostring(e)
et = ElementTree(e)
et.write('demo.xml')
# 读写excel文件
import xlrd, xlwt
book = xlrd.open_workbook('demo.xls')
book.sheets()
sheet = book.sheet_by_index(0)
rows = sheet.nrows
cols = sheet.ncols
cell = sheet.cell(0,0) #(0,0)单元格
cell.ctype
cell.value
row = sheet.row(1) #cell对象列表
data = sheet.row_values(1, 1) #第1列跳过第一格的值列表
sheet.put_cell(0, cols, xlrd.XL_CELL_TEXT, u'Total', None)
wbook = xlwt.Workbook()
wsheet = wbook.add_sheet('sheet1')
style = xlwt.easyxf('align: vertical center, horizontal center')
wsheet.write(rows,cols, sheet.cell_value(rows,cols), style)
wsheet.save('output.xls')
五. 派生内置不可变类型并修改其实例化行为
class IntTuple(tuple):
def __new__(cls, iterable): #先于__init__()调用
g = (x for x in iterable if isinstance(x, int) and x > 0)
super(IntTuple, cls).__new__(cls, g)
def __init__(self, iterable):
# 此时如果过滤iterable 无法过滤成功
super(IntTuple, self).__init__(iterable)
t = IntTuple([1, -1, 'abc', 6, ['x', 'y'], 3])
print t 无锡妇科医院排名 http://www.csyhjlyy.com/
六. 使用描述符对实例属性做类型检查
# 描述符： 包含 __get__() __set__() __delete__() 函数的类
class Attr(object):
def __init__(self, name, type_):
self.name = name
self.type_= type_
def __get__(self, instance, cls):
return instanse.__dict__[self.name]
def __set__(self, instance, value):
if not isinstance(value, self.type_):
raise TypeError('expected %s' % self.type_)
instance.__dict__[self.name] = value
def __delete__(self, instance):
del instance.__dict__[self.name]
class Person(object):
name = Attr('name', str)
age = Attr('age', int)
hgt = Attr('height', float)
p = Person()
p.name = 'Bob'
print p.name
p.age = '17' #会抛出异常
七. 在环状数据结构中管理内存
import sys
class A(object):
def __del__(self): # 当引用次数变为0时，调用析构函数
print 'in A.__del__'
a = A()
a2 = a
print sys.getrefcount(a) - 1 # 查看对象a的引用次数，参数名也引用了对象，要-1
del a
del a2
# 循环引用
class Data(object): # Data类保存node对象引用
def __init__(self, value, owner):
self.owner = owner
self.value = value
def __str__(self):
return "%s's data, value is %s" % (self.owner, self.value)
def __del__(self):
print 'in Data.__del__'
class Node(object): # Node类调用Data对象
def __init__(self, valu):
self.data = Data(value, self)
def __del__(self):
print 'in Node.__del__'
node = Node(100)
del node # 此时Data Node不会被回收掉
raw_input('wait...')
# 使用弱引用
import weakref
a_wref = weakref.ref(a)
a2 = a_wref()
class Data(object): # Data类保存Node对象引用
def __init__(self, value, owner):
self.owner = weakref.ref(owner) # 弱引用
self.value = value
def __str__(self):
return "%s's data, value is %s" % (self.owner(), self.value)
def __del__(self):
print 'in Data.__del__'
node2 = node(100)
del node2 # 此时Data Node将被回收
八. 通过实例方法名的字符串调用方法
# Circle Triangle Trctangle 求面积的方法名都不同
# 通过传方法名来调用不同的方法
# 1. getattr 获取对象属性，方法名也是属性
from lib1 import Circle
from lib2 import Triangle
from lib3 import Tectangle
def getArea(shape):
for name in ('area', 'getArea', get_area):
f = getattr(shape, name , None)
if f:
return f()
shape1 = Circle(2)
shape2 = Tirangle(3,4,5)
shape3 = Rectangle(6,4)
shapes = [shape1, shape2, shape3]
print map(getArea, shapes)
# 2. 使用opreator标准库
from opreator import methodcaller
s = "abc123abc456"
s.find('abc', 4)
methodcaller('find', 'abc', 4)(s)
九. 为创建大量实例节省内存
class Player(object):
def __init__(self, uid, name, status=0, level=1):
self.uid = uid
self.name = name
self.stat = status
self.level = level
class Player2(object):
__slots__ = ['uid', 'name', 'stat', 'level']
def __init__(self, uid, name, status=0, level=1):
self.uid = uid
self.name = name
self.stat = status
self.level = level
p1 = Player('0001', 'Jim')
p2 = Player2('0002', 'Tom')
# p1 bi p2 多两个属性 __dict__ __weakref__
# __dict__ 字典，为实例动态绑定解除新属性
# p2 则不能动态绑定属性
# __slots__ 阻止了该功能
十. 让对象支持上下文管理
# 要使用上下文管理，类中要定义 __enter__ __exit__方法，分别在with开始和结束时调用
class test(object):
...
def __enter__(self):
pass
def __exit__(self, exc_type, exc_val, exc_tb):
pass
with test() as k:
pass
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