A byte of Python

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A byte of Python

To know the basic of Python

listing 5.1 while loop

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number = 23
running = True

while(running):
	guess = int(input('Enter an integer:'))

	if guess == number:
		print("Congratulations, you guessed it .")
		print("but you do not win any prizes!")
		running = False
	elif guess < number:
		print("No it is a litter higher than that")
	else:
		print("No it is a little lower than that")
else:	
	print('Done')

listing 5.2 for loop

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for i in range(1,5):
	print(i)
else:
	print('the for loop is over')

listing break statement

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while(True):
	s = input('Enter something:')
	if(s=='quit'):
		break
	print('Length of the string is',len(s))
print('Done')

listing 5.4 continue

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while(True):
	s = input('Enter something:')
	if(s=='quit'):
		break
	if len(s)<3:
		print('Input is of sufficient length')
		continue

	print('Length of the string is',len(s))
print('Done')

listing 5.5 python

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def sayHello():
	print('Hello,World')
	#block belonging to the function

#call the function
sayHello()

#you cant define synNo after sayNo() call
def sayNo():
	print('No No')
sayNo()

listing 7.2 using function x para

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def printMax(a,b):
	if(a>b):
		print(a,'is maximum')
	else:
		print(b,'is maximum')

printMax(3,4)
x = 5
y = 7
printMax(x,y)

listing 7.3 using local variable

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def func(x):
	print('x is ', x)
	x = 2
	print('changed local x to ',x)

x = 50
func(x)

print('x is still',x)

listing 7.4 using global statement

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def globalF():
	global x
	print('x is ',x)
	x=2
	print('changed local x to ',x)

x = 50
globalF()
print('Value of x is',x)

listing 7.5 using default paras

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def say(message,times = 1):
	print(message * times)
say("Hello")
say("World",5)
#console : Hello WorldWorldWorldWorldWorld

listing 7.6 use key para

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def func(a, b = 5, c = 10):
	print('a is ',a,'and b is ',b,'and c is ',c)

func(3,7)
func(25,c = 24)
func(c = 50, a = 100)

#a is  3 and b is  7 and c is  10
#a is  25 and b is  5 and c is  24
#a is  100 and b is  5 and c is  50

listing 7.7 use return

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def maximum(x,y):
	if x>y:
		return x
	else:
		return y

print(maximum(2,3))

listing 7.8 

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def someFuntion():
    pass

listing 7.9 docStrings

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def printMax(x,y):
	'Prints the maximum of two numbers\
	The two values must be integers'
	x = int(x)
	y = int(y)

	if(x>y):
		print(x,'is Max')
	else:
		print(y,'is Max')

printMax(3,5)
print (printMax.__doc__)

listing 8.1 using System module

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import sys
print('the command line arguments are:')
for i in sys.argv:
	print(i)

print ('\n\nthe python paht is ',sys.path)

listing 8.2 using module name

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if(__name__=='__main__'):
	print('This program is being run by itself')
else:
	print('i am being imported from another module')

listing 8.3 how to use module

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#mymodule.py
def sayHi():
	print('Hi , this is my module speaking')

version = '0.1'
#End of my module.py

#usemymodule.py
import mymodule

mymodule.sayHi();
print('Version ',mymodule.version)

listing 8.4 dir()

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$python
>>>import sys
>>>dir(sys)
>>>dir()
>>>a = 5
>>>dir()
>>>del a
>>>dir()

listing 8.5 list()

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# this is my shopping list
shoplist = ["apple","mango","carrot","banana"]
print("I have",len(shoplist),"items to purchase.")
print("These items are:")
for item in shoplist:
    print(item)
print("\n I also have to buy rice.")
shoplist.append("rice")
print("My shopping list is now:  ",shoplist)

print("I will sort my list now")
shoplist.sort()
print("The first item I will buy is ", shoplist[0])
olditem = shoplist[0]
del shoplist[0]
print("I bought the ",olditem)
print("My shopping list is now ",shoplist)

listing 8.6 tuple

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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 in new zoo", new_zoo)
print("form old zoo", new_zoo[2])
print("last animal brought from old zoo is ", new_zoo[2][2])

listing 8.7 using tuple output

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age = 22

listing 8.8 using dict 

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

print("Swaroop s address is % ",ab['Swaroop'])

ab['Guido'] = 'guido@python.org'
del ab["Spammer"]
print("----------There are " ,len(ab))
for name,address in ab.items():
    print("Contact sta ",name,address)

if 'Guido' in ab:
    print("Guido address is ", ab['Guido'])

using seq

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#Filename: seq.py
shoplist =['aple','mango','carrot','banana']
#Indexing or 'Subscription' operation
print("item -0- ",shoplist[0])
print("item -1- ",shoplist[1])
print("item -2- ",shoplist[2])
print("item -3- ",shoplist[3])
print("item --1- ",shoplist[-1])
print("item --2- ",shoplist[-2])

#Slicing on a list
print('Item 1 to 3 is ',shoplist[1:3])
print('Item 2 to end is ',shoplist[2:])
print('Item 1 to -1 is', shoplist[1:-1])
print('Item start to end is ',shoplist[:])

#Slicing on a string
name = 'swaroop'
print('characters 1 to 3 is ',name[1:3])
print('characters 2 to end is',name[2:])
print('characters 1 ~ -1 is ',name[1:-1])
print('characters start to end is ',name[:])

listing 9.6 using object and reference

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# reference
print("Simple assignment")
shoplist =['apple','mango','carrot','banana']
mylist = shoplist

del shoplist[0]

print('shoplist is ',shoplist)
print('mylist is ',mylist)

print('Copy by making a full slice')
mylist = shoplist[:]
del mylist[0]

print('shoplist is ',shoplist)
print('mylist is ',mylist)

实际上就是一个是引用类型，一个是新对象？如果想要

listing 9.7 str methods

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# str_methods.py

name = 'Swaroop'

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))

listing 11.1 use class

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#simple class .py
class Person:
    pass

p = Person()
print(p)

listing 11.2 use object method

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#method.py
class Person:
    def sayHi(self):
        print('Hello,how are you?')

p = Person()
p.sayHi()
Person().sayHi()
#Person().sayHi()

listing 11.3 using init

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class Person:
    def __init__(self,name):
        self.name = name
    def sayHi(self):
        print('Hello,my name is ',self.name)

p = Person("Harry")
p.sayHi()
Person('Swaroop').sayHi()

listing 11.4 use class and object var

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#objvar.py
class Person:
    "Represents a person."
    population =0

    def __init__(self,name):
        'Initializes the Persons data'
        self.name = name
        print('Initializing %s' % self.name)
        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('The is still %d' % Person.population)
    def sayHi(self):
        'Gretting by the person'
        print('Hi , my name is %s' % self.name)

    def howMany(self):
        if Person.population == 1:
            print('Iam the last 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()

继承

listing 11.1 use inherit

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#inherit.py
class SchoolMember:
    'Represents any school member'
    def __init__(self,name,age):
        self.name = name
        self.age = age
        print('Initialized School Member: %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',40,300000)
s = Student('Swaroop',22,76)

print()
members = [t,s]
for member in members:
    member.tell()

文件IO

listing 12.1 use_file.py

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#using_file.py
poem ='''\
Programming is fun
When the work is done
if you wanna make your work also fun:
     use PyCharm!
     '''

f = open('poem.txt','w') #open for writing
f.write(poem)
f.close()

f = open('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

数据持久化 cPickle

listing Save and load

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#Filename:pickling.py
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 = open(shoplistfile,'wb')
p.dump(shoplist,f,-1)
p.dump(shoplist,f)
f.close()

del shoplist #remove the shoplist

# Read back from the storage
f = open(shoplistfile,'rb')
storedlist = p.load(f)
print(storedlist)

list 13.1 try catch

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try:
    fh = open("testfile", "w")
    fh.write("这是一个测试文件，用于测试异常!!")
except IOError:
    print('no found')
else:
    print("write success")
    fh.close()

listing 13.2

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#filename: raising.py
import sys

class ShortInputException(Exception):
    '''A user-defined exception class'''
    def __init__(self,length,atleast):
        Exception.__init__(self)
        self.length = length
        self.atleast = atleast

try:
    s = input("Enter Something-->")
    if len(s) < 3:
        raise ShortInputException(len(s),3)
except EOFError:
    print('\nWhy did you do an EOF on me')
except ShortInputException:
    print('Short Input Exception: the input is ')
else:
    print('No exceptin was raised')

listing 13.3 use finally

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import time
try:
    f = open('poem.txt')
    while True:
        line = f.readline()
        if len(line) ==0:
            break;
        time.sleep(2)
        print(line)
finally:
    f.close()
    print('Cleaning up ... closed the file')

listing 14.1 use sys.argv

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# filename: cat.py
import sys


def readfile(_filename):
    """print a file to the standard output"""
    f = open(_filename)
    while True:
        line = f.readline()
        if len(line) == 0:
            break
        print(line)
    f.close()
# Script starts from here


if len(sys.argv) < 2:
    print('No action specified')
    sys.exit()
if sys.argv[1].startswith('--'):
    option = sys.argv[1][2:]
    if option == 'version' :
        print('Version 1.2')
    elif option == 'help':
        print('''This program prints files to the standard output
        Any number of files can be specified
        Options include:
        --version: Prints the version number
        --help : display this help''')
    else:
        print("Unknown option")
    sys.exit()
else:
    for filename in sys.argv[1:]:
        readfile(filename)

listing extra uss sys.argv in C#

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namespace hohoho
{
    public class ccc
    {
            static void Main(string[] args)
        {
            for (int i = 0; i < args.Length; i++)
            {
                if(args[i].StartsWith("--"))
                {
                    switch (args[i])
                    {
                        case "--version" :
                            System.Console.WriteLine("ccc version: 1.20");
                            break;
                        case "--dd" :
                            System.Console.WriteLine("I love dd forever");
                            break;
                        default:
                            break;
                    }
                }else
                {
                    continue;
                }
            }
            if (args.Length == 0)
            {
                System.Console.WriteLine("Nonsence");
            }
        }
    }
}

listing 15.1 use comprehension

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# filename: list_comprehension.py
_listOne = [2, 3, 4]
_listTwo = [2 * i for i in _listOne if i > 2]
print(_listTwo)

listing 15.2 use lambda

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# filename: use lambda
def make_repeater(n):
    return lambda s: s * n


twice = make_repeater(2)

print(twice('world'))
print(twice(5))

只能使用表达式在lambda中