简明python教程笔记

 

 

自然字符串

如果你想要指示某些不需要如转义符那样的特别处理的字符串，那么你需要指定一个自然字符串。自然字符串通过给字符串加上前缀r或R来指定。

r"Newlines are indicated by \n"

 

在文件头加上linux下运行python的主程序模块和文件名

#!/usr/bin/python
#Filename:test.py

 

打印DocString（文档字符串）是个好习惯

#!/usr/bin/python
#Filename:test.py

def printMax(x, y):
    '''Prints the maximum of two numbers.

    The two values must be integers.'''
    x = int(x) # convert to integers, if possible
    y = int(y)
    if x > y:
        print x, 'is maximum'
    else:
        print y, 'is maximum'

printMax(3, 5)
print printMax.__doc__

Result

 

 主模块入口Sample

#!/usr/bin/python
# Filename: using_name.py
if __name__ == '__main__':
    print 'This program is being run by itself'
else:
    print 'I am being imported from another module'

 

构建自己的模块

mymodule

#!/usr/bin/python
# Filename: mymodule.py
def sayhi():
print 'Hi, this is mymodule speaking.'
version = '0.1'
# End of mymodule.py

import的主module

#!/usr/bin/python
# Filename: mymodule_demo.py
import mymodule
mymodule.sayhi()
print 'Version', mymodule.version

 

数据结构

列表，即Javascript中的数组，可以对它进行增删改查的操作

#!/usr/bin/python
# Filename: using_list.py

# This is my shopping list
shoplist = ['apple', 'mango', 'carrot', 'banana']

print 'I have', len(shoplist),'items to purchase.' #length

print 'These items are:', # Notice the comma at end of the line
for item in shoplist: #for-in circle
    print item,

print '\nI also have to buy rice.'
shoplist.append('rice') #append element
print 'My shopping list is now', shoplist

print 'I will sort my list now'
shoplist.sort() #sort elements
print 'Sorted shopping list is', shoplist

print 'The first item I will buy is', shoplist[0] #get element by index
olditem = shoplist[0]
del shoplist[0] #delete element
print 'I bought the', olditem
print 'My shopping list is now', shoplist

Result

 

元组，和列表类似，但是不能修改，即为不能修改的列表，用()包裹。

元组可以直接输出，定义中可以直接包含其他元组

类似于C++中的多维数组

#!/usr/bin/python
# Filename: using_tuple.py

zoo = ('wolf', 'elephant', 'penguin')
print 'Number of animals in the zoo is', len(zoo)

new_zoo = ('monkey', 'dolphin', zoo)
print 'Number of animals in the new zoo is', len(new_zoo)
print 'All animals in new zoo are', new_zoo
print 'Animals brought from old zoo are', new_zoo[2]
print 'Last animal brought from old zoo is', new_zoo[2][2]

Result

 

元组一般用于打印

#!/usr/bin/python
# Filename: print_tuple.py

age = 22
name = 'Swaroop'
print '%s is %d years old' % (name, age)
print 'Why is %s playing with that python?' % name

 

字典，类似于Javascript里的Object，key/value键值对，Hash表

#!/usr/bin/python
#Filename:test.py

#ab is short for 'a'ddress 'b'ook

ab={
    'Swaroop' : 'swaroopch@byteofpython.info',
    'Larry' : 'larry@wall.org',
    'Matsumoto' : 'matz@ruby-lang.org',
    'Spammer' : 'spammer@hotmail.com'
    }

print "Swaroop's address is %s" % ab['Swaroop']

#Adding a key/value pair
ab['Guido'] = 'guido@python.org'

#Deleting a key/value pair
del ab['Spammer']

print '\nThere are %d contacts in the address-book\n' % len(ab)

for name,address in ab.items():
    print 'Contact %s at %s' %(name,address)

if 'Guido' in ab: #OR ab.has_key(Guido)
    print "\nGuido's address is %s" %ab['Guido']

Result

 

列表、元组和字符串都是序列，但是序列是什么，它们为什么如此特别呢？序列的两个主要特点是索引操作符和切片操作符。索引操作符让我们可以从序列中抓取一个特定项目。切片操作符让我们能够获取序列的一个切片，即一部分序列。

#!/usr/bin/python
# Filename: seq.py

shoplist = ['apple', 'mango', 'carrot', 'banana']

# Indexing or 'Subscription' operation
print 'Item 0 is', shoplist[0] #Item 0 is apple
print 'Item 1 is', shoplist[1] #Item 1 is mango
print 'Item 2 is', shoplist[2] #Item 2 is carrot
print 'Item 3 is', shoplist[3] #Item 3 is banana
print 'Item -1 is', shoplist[-1] #Item -1 is banana
print 'Item -2 is', shoplist[-2] #Item -2 is carrot

# Slicing on a list
print 'Item 1 to 3 is', shoplist[1:3] #Item 1 to 3 is ['mango', 'carrot']
print 'Item 2 to end is', shoplist[2:] #Item 2 to end is ['carrot', 'banana']
print 'Item 1 to -1 is', shoplist[1:-1] #Item 1 to -1 is ['mango', 'carrot']
print 'Item start to end is', shoplist[:] #Item start to end is ['apple', 'mango', 'carrot', 'banana']

# Slicing on a string
name = 'swaroop'
print 'characters 1 to 3 is', name[1:3] #characters 1 to 3 is wa
print 'characters 2 to end is', name[2:] #characters 2 to end is aroop
print 'characters 1 to -1 is', name[1:-1] #characters 1 to -1 is waroo
print 'characters start to end is', name[:] #characters start to end is swaroop

Result

 

引用，类似于C++的指针，如果我们把一个列表赋值给一个新变量，实际是新变量指向列表的内存地址，如果我们把一个序列复制给一个新变量，这只是Copy操作。

#!/usr/bin/python
# Filename: reference.py

print 'Simple Assignment'
shoplist = ['apple', 'mango', 'carrot', 'banana']
mylist = shoplist # mylist is just another name pointing to the same object!
del shoplist[0]
print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that both shoplist and mylist both print the same list without
# the 'apple' confirming that they point to the same object
print 'Copy by making a full slice'

mylist = shoplist[:] # make a copy by doing a full slice
del mylist[0] # remove first item
print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that now the two lists are different

Result

 

常用的字符串方法

#!/usr/bin/python
# Filename: str_methods.py

name = 'Swaroop' # This is a string object
if name.startswith('Swa'):
print 'Yes, the string starts with "Swa"'

if 'a' in name:
print 'Yes, it contains the string "a"'

if name.find('war') != -1:
print 'Yes, it contains the string "war"'

delimiter = '_*_'
mylist = ['Brazil', 'Russia', 'India', 'China']
print delimiter.join(mylist)

 

 

 

编写一个备份文件的Python脚本

设计思路

1. 需要备份的文件和目录由一个列表指定。

2. 备份应该保存在主备份目录中。

3. 文件备份成一个zip文件。

4. zip存档的名称是当前的日期和时间。

5. 我们使用标准的zip命令，它通常默认地随Linux/Unix发行版提供。Windows用户可以使用Info-Zip程序。注意你可以使用任何地存档命令，只要它有命令行界面就可以了，那样的话我们可以从我们的脚本中传递参数给它。

Code

#!/usr/bin/python
# Filename: backup_ver1.py

import os
import time

# 1. The files and directories to be backed up are specified in a list.
source = ['/home/swaroop/byte', '/home/swaroop/bin']
# If you are using Windows, use source = [r'C:\Documents', r'D:\Work'] or something like that

# 2. The backup must be stored in a main backup directory
target_dir = '/mnt/e/backup/' # Remember to change this to what you will be using

# 3. The files are backed up into a zip file.
# 4. The name of the zip archive is the current date and time
target = target_dir + time.strftime('%Y%m%d%H%M%S') + '.zip'

# 5. We use the zip command (in Unix/Linux) to put the files in a zip archive
zip_command = "zip -qr '%s' %s" % (target, ' '.join(source))

# Run the backup
if os.system(zip_command) == 0:
    print 'Successful backup to', target
else:
    print 'Backup FAILED'

 

 

 

面向对象

类与对象的方法

举个简单的例子就能看懂，书上的缩进写的一团糟，看起来有点类，手打一遍，发现Python真的很优雅！

#!/usr/bin/python
#Filename:test.py

class Person:
    '''Represents a person.'''
    population = 0

    def __init__(self,name):
        '''Initializes the person's data.'''
        self.name = name
        print '(Initializing %s)' %self.name

        #When this person is created,he/she
        #adds to the population
        Person.population += 1

    def __del__(self):
        '''I am dying.'''
        print '%s says bye.' %self.name

        Person.population -= 1

        if Person.population == 0:
            print 'I am the last one.'
        else:
            print 'There are strill %d people left.' %Person.population

    def sayHi(self):
        '''Greeting by the person.

        Really,that's all it does.'''
        print 'Hi,my name is %s.' %self.name

    def howMany(self):
        '''Prints the current population.'''
        if Person.population == 1:
            print 'I am the only person here.'
        else:
            print 'We have %d persons here.' %Person.population


swaroop = Person('Swaroop')
swaroop.sayHi()
swaroop.howMany()

kalam = Person('Abdul Kalam')
kalam.sayHi()
kalam.howMany()

swaroop.sayHi()
swaroop.howMany()

Result

 

继承

#!/usr/bin/python
#Filename:test.py

class SchoolMember:
    '''Represents any school member.'''
    def __init__(self,name,age):
        self.name = name
        self.age = age
        print '(Initialized SchoolMember: %s)' %self.name

    def tell(self):
        '''Tell my details.'''
        print 'Name:"%s" Age:"%s"' %(self.name,self.age)



class Teacher(SchoolMember):
    '''Represents a teacher.'''
    def __init__(self,name,age,salary):
        SchoolMember.__init__(self,name,age)
        self.salary = salary
        print '(Initialized Teacher: %s)' %self.name

    def tell(self):
        SchoolMember.tell(self)
        print 'Salary:"%d"' %self.salary




class Student(SchoolMember):
    '''Represents a student.'''
    def __init__(self,name,age,marks):
        SchoolMember.__init__(self,name,age)
        self.marks = marks
        print '(Initialized Student: %s)' %self.name

    def tell(self):
        SchoolMember.tell(self)
        print 'Marks:"%d"' %self.marks



t = Teacher('Mrs.Shrividya',40,30000)
s = Student('Swaroop',22,75)

print #prints a blank line

members = [t,s]
for member in members:
    member.tell() #works for both Teachers and Students
        

Result

 

 

输入输出

文件

你可以通过创建一个file类的对象来打开一个文件，分别使用file类的read、readline或write方法来恰当地读写文件。对文件的读写能力依赖于你在打开文件时指定的模式。最后当你完成对文件的操作的时候，你调用close方法来告诉Python我们完成了对文件的使用。

#!/usr/bin/python
#Filename:test.py

poem = '''\
Programming is fun
When the work is done
if you wanna make your work also fun:
use Python!
'''

f = file('poem.txt','w') #open for 'w'rting
f.write(poem) #write text to file
f.close() #close the file

f = file('poem.txt')
#if no mode is specified,'r'ead mode is assumed by default
while True:
    line = f.readline()
    if len(line) == 0:#Zero length indicates EOF
        break
    print line,
    #Notice comma to avoid automatic newline added by Python

f.close() #close the file

 

储存与取储存 dump()&load()

Python提供一个标准的模块，称为pickle。使用它你可以在一个文件中储存任何Python对象，之后你又可以把它完整无缺地取出来。这被称为 持久地 储存对象。

还有另一个模块称为cPickle，它的功能和pickle模块完全相同，只不过它是用C语言编写的，因此要快得多（比pickle快1000倍）。你可以使用它们中的任一个，而我们在这里将使用cPickle模块。记住，我们把这两个模块都简称为pickle模块。

#!/usr/bin/python
#Filename:test.py

import cPickle as p
#import pickle as p

shoplistfile = 'shoplist.data'
# the name of the file where we will store the object

shoplist = ['apple', 'mango', 'carrot']

# Write to the file
f = file(shoplistfile, 'w')
p.dump(shoplist, f) # dump the object to a file
f.close()

del shoplist # remove the shoplist

# Read back from the storage
f = file(shoplistfile)
storedlist = p.load(f)
print storedlist
        

 

 

异常

try...except的用法

#!/usr/bin/python
#Filename:test.py

import sys

try:
    s = raw_input('Enter something --> ')
except EOFError:
    print '\nWhy did you do an EOF on me?'
    sys.exit() # exit the program
except:
    print '\nSome error/exception occurred.'
    # here, we are not exiting the program

print 'Done'

 

 

http://pythonguidecn.readthedocs.org/zh/latest/

http://old.sebug.net/paper/books/LearnPythonTheHardWay/