控制台交互
可以根据 __name__ 关键字来判断是否是直接使用 python 命令执行某个脚本，还是外部引用；Google 开源的 fire 也是不错的快速将某个类封装为命令行工具的框架：
import fire
class Calculator(object):
"""A simple calculator class."""
def double(self, number):
return 2 * number
if __name__ == '__main__':
fire.Fire(Calculator)
# python calculator.py double 10 # 20
# python calculator.py double --number=15 # 30
模块
Python 中的模块（Module）即是 Python 源码文件，其可以导出类、函数与全局变量；当我们从某个模块导入变量时，函数名往往就是命名空间（Namespace）。而 Python 中的包（Package）则是模块的文件夹，往往由 __init__.py 指明某个文件夹为包:
Package 可以为某个目录下所有的文件设置统一入口:
someDir/
main.py
subModules/
__init__.py
subA.py
subSubModules/
__init__.py
subSubA.py
# subA.py
def subAFun():
print('Hello from subAFun')
def subAFunTwo():
print('Hello from subAFunTwo')
# subSubA.py
def subSubAFun():
print('Hello from subSubAFun')
def subSubAFunTwo():
print('Hello from subSubAFunTwo')
# __init__.py from subDir
# Adds 'subAFun()' and 'subAFunTwo()' to the 'subDir' namespace
from .subA import *
# The following two import statement do the same thing, they add 'subSubAFun()' and 'subSubAFunTwo()' to the 'subDir' namespace. The first one assumes '__init__.py' is empty in 'subSubDir', and the second one, assumes '__init__.py' in 'subSubDir' contains 'from .subSubA import *'.
# Assumes '__init__.py' is empty in 'subSubDir'
# Adds 'subSubAFun()' and 'subSubAFunTwo()' to the 'subDir' namespace
from .subSubDir.subSubA import *
# Assumes '__init__.py' in 'subSubDir' has 'from .subSubA import *'
# Adds 'subSubAFun()' and 'subSubAFunTwo()' to the 'subDir' namespace
from .subSubDir import *
# __init__.py from subSubDir
# Adds 'subSubAFun()' and 'subSubAFunTwo()' to the 'subSubDir' namespace
from .subSubA import *
# main.py
import subDir
subDir.subAFun() # Hello from subAFun
subDir.subAFunTwo() # Hello from subAFunTwo
subDir.subSubAFun() # Hello from subSubAFun
subDir.subSubAFunTwo() # Hello from subSubAFunTwo
循环遍历
for-in 可以用来遍历数组与字典：
Number: 数值类型
x = 3
print type(x) # Prints "<type 'int'>"
print x # Prints "3"
print x + 1 # Addition; prints "4"
print x - 1 # Subtraction; prints "2"
print x * 2 # Multiplication; prints "6"
print x ** 2 # Exponentiation; prints "9"
x += 1
print x # Prints "4"
x *= 2
print x # Prints "8"
y = 2.5
print type(y) # Prints "<type 'float'>"
print y, y + 1, y * 2, y ** 2 # Prints "2.5 3.5 5.0 6.25"
Python 字符串支持分片、模板字符串等常见操作:
var1 = 'Hello World!'
var2 = "Python Programming"
print "var1[0]: ", var1[0]
print "var2[1:5]: ", var2[1:5]
# var1[0]: H
# var2[1:5]: ytho
print "My name is %s and weight is %d kg!" % ('Zara', 21)
# My name is Zara and weight is 21 kg!
str[0:4]
len(str)
string.replace("-", " ")
",".join(list)
"hi {0}".format('j')
str.find(",")
str.index(",") # same, but raises IndexError
str.count(",")
str.split(",")
str.lower()
str.upper()
str.title()
str.lstrip()
str.rstrip()
str.strip()
str.islower()
# 移除所有的特殊字符
re.sub('[^A-Za-z0-9]+', '', mystring)
集合类型
List: 列表
Operation: 创建增删
list 是基础的序列类型：
可以使用 pop、slices、del、remove 等移除列表中元素：
myList = [10,20,30,40,50]
# 弹出第二个元素
myList.pop(1) # 20
# myList: myList.pop(1)
# 如果不加任何参数，则默认弹出最后一个元素
myList.pop()
# 使用 slices 来删除某个元素
a = [ 1, 2, 3, 4, 5, 6 ]
index = 3 # Only Positive index
a = a[:index] + a[index+1 :]
# 根据下标删除元素
myList = [10,20,30,40,50]
rmovIndxNo = 3
del myList[rmovIndxNo] # myList: [10, 20, 30, 50]
# 使用 remove 方法，直接根据元素删除
letters = ["a", "b", "c", "d", "e"]
numbers.remove(numbers[1])
print(*letters) # used a * to make it unpack you don't have to
Comprehensions: 变换
Python 中同样可以使用 map、reduce、filter，map 用于变换数组:
字典类型
创建增删
d = {'cat': 'cute', 'dog': 'furry'} # 创建新的字典
print d['cat'] # 字典不支持点（Dot）运算符取值
如果需要合并两个或者多个字典类型：
# python 3.5
z = {**x, **y}
# python 2.7
def merge_dicts(*dict_args):
"""
Given any number of dicts, shallow copy and merge into a new dict,
precedence goes to key value pairs in latter dicts.
"""
result = {}
for dictionary in dict_args:
result.update(dictionary)
return result
其他序列类型
集合
# Same as {"a", "b","c"}
normal_set = set(["a", "b","c"])
# Adding an element to normal set is fine
normal_set.add("d")
print("Normal Set")
print(normal_set)
# A frozen set
frozen_set = frozenset(["e", "f", "g"])
print("Frozen Set")
print(frozen_set)
# Uncommenting below line would cause error as
# we are trying to add element to a frozen set
# frozen_set.add("h")
函数
函数定义
Python 中的函数使用 def 关键字进行定义，譬如:
def sign(x):
if x > 0:
return 'positive'
elif x < 0:
return 'negative'
else:
return 'zero'
for x in [-1, 0, 1]:
print sign(x)
# Prints "negative", "zero", "positive"
Python 支持运行时创建动态函数，也即是所谓的 lambda 函数：
def f(x): return x**2
# 等价于
g = lambda x: x**2
参数
Option Arguments: 不定参数
def example(a, b=None, *args, **kwargs):
print a, b
print args
print kwargs
example(1, "var", 2, 3, word="hello")
# 1 var
# (2, 3)
# {'word': 'hello'}
a_tuple = (1, 2, 3, 4, 5)
a_dict = {"1":1, "2":2, "3":3}
example(1, "var", *a_tuple, **a_dict)
# 1 var
# (1, 2, 3, 4, 5)
# {'1': 1, '2': 2, '3': 3}
生成器
def simple_generator_function():
yield 1
yield 2
yield 3
for value in simple_generator_function():
print(value)
# 输出结果
# 1
# 2
# 3
our_generator = simple_generator_function()
next(our_generator)
# 1
next(our_generator)
# 2
next(our_generator)
#3
# 生成器典型的使用场景譬如无限数组的迭代
def get_primes(number):
while True:
if is_prime(number):
yield number
number += 1
装饰器
装饰器是非常有用的设计模式:
# 简单装饰器
from functools import wraps
def decorator(func):
@wraps(func)
def wrapper(*args, **kwargs):
print('wrap function')
return func(*args, **kwargs)
return wrapper
@decorator
def example(*a, **kw):
pass
example.__name__ # attr of function preserve
# 'example'
# Decorator
# 带输入值的装饰器
from functools import wraps
def decorator_with_argument(val):
def decorator(func):
@wraps(func)
def wrapper(*args, **kwargs):
print "Val is {0}".format(val)
return func(*args, **kwargs)
return wrapper
return decorator
@decorator_with_argument(10)
def example():
print "This is example function."
example()
# Val is 10
# This is example function.
# 等价于
def example():
print "This is example function."
example = decorator_with_argument(10)(example)
example()
# Val is 10
# This is example function.
类方法与静态方法
class example(object):
@classmethod
def clsmethod(cls):
print "I am classmethod"
@staticmethod
def stmethod():
print "I am staticmethod"
def instmethod(self):
print "I am instancemethod"
ex = example()
ex.clsmethod()
# I am classmethod
ex.stmethod()
# I am staticmethod
ex.instmethod()
# I am instancemethod
example.clsmethod()
# I am classmethod
example.stmethod()
# I am staticmethod
example.instmethod()
# Traceback (most recent call last):
# File "", line 1, in
# TypeError: unbound method instmethod() ...
对象
实例化
属性操作
Python 中对象的属性不同于字典键，可以使用点运算符取值，直接使用 in 判断会存在问题:
class A(object):
@property
def prop(self):
return 3
a = A()
print "'prop' in a.__dict__ =", 'prop' in a.__dict__
print "hasattr(a, 'prop') =", hasattr(a, 'prop')
print "a.prop =", a.prop
# 'prop' in a.__dict__ = False
# hasattr(a, 'prop') = True
# a.prop = 3
建议使用 hasattr、getattr、setattr 这种方式对于对象属性进行操作:
class Example(object):
def __init__(self):
self.name = "ex"
def printex(self):
print "This is an example"
# Check object has attributes
# hasattr(obj, 'attr')
ex = Example()
hasattr(ex,"name")
# True
hasattr(ex,"printex")
# True
hasattr(ex,"print")
# False
# Get object attribute
# getattr(obj, 'attr')
getattr(ex,'name')
# 'ex'
# Set object attribute
# setattr(obj, 'attr', value)
setattr(ex,'name','example')
ex.name
# 'example'
异常与测试
异常处理
Context Manager - with
with 常用于打开或者关闭某些资源:
host = 'localhost'
port = 5566
with Socket(host, port) as s:
while True:
conn, addr = s.accept()
msg = conn.recv(1024)
print msg
conn.send(msg)
conn.close()
单元测试
from __future__ import print_function
import unittest
def fib(n):
return 1 if n<=2 else fib(n-1)+fib(n-2)
def setUpModule():
print("setup module")
def tearDownModule():
print("teardown module")
class TestFib(unittest.TestCase):
def setUp(self):
print("setUp")
self.n = 10
def tearDown(self):
print("tearDown")
del self.n
@classmethod
def setUpClass(cls):
print("setUpClass")
@classmethod
def tearDownClass(cls):
print("tearDownClass")
def test_fib_assert_equal(self):
self.assertEqual(fib(self.n), 55)
def test_fib_assert_true(self):
self.assertTrue(fib(self.n) == 55)
if __name__ == "__main__":
unittest.main()
存储
文件读写
路径处理
Python 内置的 __file__ 关键字会指向当前文件的相对路径，可以根据它来构造绝对路径，或者索引其他文件:
# 获取当前文件的相对目录
dir = os.path.dirname(__file__) # src\app
## once you're at the directory level you want, with the desired directory as the final path node:
dirname1 = os.path.basename(dir)
dirname2 = os.path.split(dir)[1] ## if you look at the documentation, this is exactly what os.path.basename does.
# 获取当前代码文件的绝对路径，abspath 会自动根据相对路径与当前工作空间进行路径补全
os.path.abspath(os.path.dirname(__file__)) # D:\WorkSpace\OWS\tool\ui-tool-svn\python\src\app
# 获取当前文件的真实路径
os.path.dirname(os.path.realpath(__file__)) # D:\WorkSpace\OWS\tool\ui-tool-svn\python\src\app
# 获取当前执行路径
os.getcwd()
可以使用 listdir、walk、glob 模块来进行文件枚举与检索：
# 仅列举所有的文件
from os import listdir
from os.path import isfile, join
onlyfiles = [f for f in listdir(mypath) if isfile(join(mypath, f))]
# 使用 walk 递归搜索
from os import walk
f = []
for (dirpath, dirnames, filenames) in walk(mypath):
f.extend(filenames)
break
# 使用 glob 进行复杂模式匹配
import glob
print(glob.glob("/home/adam/*.txt"))
# ['/home/adam/file1.txt', '/home/adam/file2.txt', .... ]
简单文件读写
# 可以根据文件是否存在选择写入模式
mode = 'a' if os.path.exists(writepath) else 'w'
# 使用 with 方法能够自动处理异常
with open("file.dat",mode) as f:
f.write(...)
...
# 操作完毕之后记得关闭文件
f.close()
# 读取文件内容
message = f.read()
复杂格式文件
JSON
import json
# Writing JSON data
with open('data.json', 'w') as f:
json.dump(data, f)
# Reading data back
with open('data.json', 'r') as f:
data = json.load(f)
XML
我们可以使用 lxml 来解析与处理 XML 文件，本部分即对其常用操作进行介绍。lxml 支持从字符串或者文件中创建 Element 对象：
from lxml import etree
# 可以从字符串开始构造
xml = '<a xmlns="test"><b xmlns="test"/></a>'
root = etree.fromstring(xml)
etree.tostring(root)
# b'<a xmlns="test"><b xmlns="test"/></a>'
# 也可以从某个文件开始构造
tree = etree.parse("doc/test.xml")
# 或者指定某个 baseURL
root = etree.fromstring(xml, base_url="http://where.it/is/from.xml")
其提供了迭代器以对所有元素进行遍历：
# 遍历所有的节点
for tag in tree.iter():
if not len(tag):
print tag.keys() # 获取所有自定义属性
print (tag.tag, tag.text) # text 即文本子元素值
# 获取 XPath
for e in root.iter():
print tree.getpath(e)
lxml 支持以 XPath 查找元素，不过需要注意的是，XPath 查找的结果是数组，并且在包含命名空间的情况下，需要指定命名空间：
root.xpath('//page/text/text()',ns={prefix:url})
# 可以使用 getparent 递归查找父元素
el.getparent()
lxml 提供了 insert、append 等方法进行元素操作：
# append 方法默认追加到尾部
st = etree.Element("state", name="New Mexico")
co = etree.Element("county", name="Socorro")
st.append(co)
# insert 方法可以指定位置
node.insert(0, newKid)
Excel
可以使用 [xlrd]() 来读取 Excel 文件，使用 xlsxwriter 来写入与操作 Excel 文件。
# 读取某个 Cell 的原始值
sh.cell(rx, col).value
# 创建新的文件
workbook = xlsxwriter.Workbook(outputFile)
worksheet = workbook.add_worksheet()
# 设置从第 0 行开始写入
row = 0
# 遍历二维数组，并且将其写入到 Excel 中
for rowData in array:
for col, data in enumerate(rowData):
worksheet.write(row, col, data)
row = row + 1
workbook.close()
文件系统
对于高级的文件操作，我们可以使用 Python 内置的 shutil
# 递归删除 appName 下面的所有的文件夹
shutil.rmtree(appName)
网络交互
Requests
Requests 是优雅而易用的 Python 网络请求库:
import requests
r = requests.get('https://api.github.com/events')
r = requests.get('https://api.github.com/user', auth=('user', 'pass'))
r.status_code
# 200
r.headers['content-type']
# 'application/json; charset=utf8'
r.encoding
# 'utf-8'
r.text
# u'{"type":"User"...'
r.json()
# {u'private_gists': 419, u'total_private_repos': 77, ...}
r = requests.put('http://httpbin.org/put', data = {'key':'value'})
r = requests.delete('http://httpbin.org/delete')
r = requests.head('http://httpbin.org/get')
r = requests.options('http://httpbin.org/get')
数据存储
MySQL
import pymysql.cursors
# Connect to the database
connection = pymysql.connect(host='localhost',
user='user',
password='passwd',
db='db',
charset='utf8mb4',
cursorclass=pymysql.cursors.DictCursor)
try:
with connection.cursor() as cursor:
# Create a new record
sql = "INSERT INTO `users` (`email`, `password`) VALUES (%s, %s)"
cursor.execute(sql, ('[email protected]', 'very-secret'))
# connection is not autocommit by default. So you must commit to save
# your changes.
connection.commit()
with connection.cursor() as cursor:
# Read a single record
sql = "SELECT `id`, `password` FROM `users` WHERE `email`=%s"
cursor.execute(sql, ('[email protected]',))
result = cursor.fetchone()
print(result)
finally:
connection.close()
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