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Python简明入门教程

本文实例讲述了Python简明入门教程。分享给大家供大家参考。具体如下:

一、基本概念

1、数

在Python中有4种类型的数——整数、长整数、浮点数和复数。
(1)2是一个整数的例子。
(2)长整数不过是大一些的整数。
(2)3.23和52.3E-4是浮点数的例子。E标记表示10的幂。在这里,52.3E-4表示52.3 * 10-4。
(4)(-5+4j)和(2.3-4.6j)是复数的例子。

2、字符串

(1)使用单引号(')
(2)使用双引号(")
(3)使用三引号('''或""")
利用三引号,你可以指示一个多行的字符串。你可以在三引号中自由的使用单引号和双引号。例如:

'''This is a multi-line string. This is the first line.This is the second line."What's your name," I asked.He said "Bond, James Bond."'''

(4)转义符
(5)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。例如r"Newlines are indicated by \n"。

3、逻辑行与物理行
一个物理行中使用多于一个逻辑行,需要使用分号(;)来特别地标明这种用法。一个物理行只有一个逻辑行可不用分号

二、控制流

1、if

块中不用大括号,条件后用分号,对应elif和else

if guess == number:  print 'Congratulations, you guessed it.' # New block starts hereelif guess  number:  print 'No, it is a little higher than that' # Another blockelse:  print 'No, it is a little lower than that'

2、while

用分号,可搭配else

while running:  guess = int(raw_input('Enter an integer : '))  if guess == number:    print 'Congratulations, you guessed it.'    running = False # this causes the while loop to stop  elif guess  number:    print 'No, it is a little higher than that'  else:    print 'No, it is a little lower than that'else:  print 'The while loop is over.'  # Do anything else you want to do here

3、for
用分号,搭配else

for i in range(1, 5):  print ielse:  print 'The for loop is over'

4、break和continue
同C语言

三、函数

1、定义与调用

def sayHello():  print 'Hello World!' # block belonging to the functionsayHello() # call the function

2、函数形参
类C语言

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

3、局部变量
加global可申明为全局变量

4、默认参数值

def say(message, times = 1):  print message * times

5、关键参数
如果某个函数有许多参数,而只想指定其中的一部分,那么可以通过命名来为这些参数赋值——这被称作 关键参数 ——使用名字(关键字)而不是位置来给函数指定实参。这样做有两个 优势 ——一,由于不必担心参数的顺序,使用函数变得更加简单了。二、假设其他参数都有默认值,可以只给我们想要的那些参数赋值。

def func(a, b=5, c=10):  print 'a is', a, 'and b is', b, 'and c is', cfunc(3, 7)func(25, c=24)func(c=50, a=100)

6、return

四、模块

1、使用模块

import sysprint 'The command line arguments are:'for i in sys.argv:  print i

如果想要直接输入argv变量到程序中(避免在每次使用它时打sys.),可以使用from sys import argv语句

2、dir()函数
可以使用内建的dir函数来列出模块定义的标识符。标识符有函数、类和变量。

五、数据结构

1、列表

shoplist = ['apple', 'mango', 'carrot', 'banana']print 'I have', len(shoplist),'items to purchase.'print 'These items are:', # Notice the comma at end of the linefor item in shoplist:  print item,print '\nI also have to buy rice.'shoplist.append('rice')print 'My shopping list is now', shoplistprint 'I will sort my list now'shoplist.sort()print 'Sorted shopping list is', shoplistprint 'The first item I will buy is', shoplist[0]olditem = shoplist[0]del shoplist[0]print 'I bought the', olditemprint 'My shopping list is now', shoplist

2、元组
元组和列表十分类似,只不过元组和字符串一样是不可变的即你不能修改元组。

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_zooprint 'Animals brought from old zoo are', new_zoo[2]print 'Last animal brought from old zoo is', new_zoo[2][2]

像一棵树

元组与打印

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

3、字典

类似哈希

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 pairab['Guido'] = 'guido@python.org'# Deleting a key/value pairdel 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']

4、序列

列表、元组和字符串都是序列。序列的两个主要特点是索引操作符和切片操作符。

shoplist = ['apple', 'mango', 'carrot', 'banana']# Indexing or 'Subscription' operationprint 'Item 0 is', shoplist[0]print 'Item 1 is', shoplist[1]print 'Item -1 is', shoplist[-1]print 'Item -2 is', shoplist[-2]# Slicing on a listprint '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 stringname = 'swaroop'print 'characters 1 to 3 is', name[1:3]print 'characters 2 to end is', name[2:]print 'characters 1 to -1 is', name[1:-1]print 'characters start to end is', name[:]

5、参考

当你创建一个对象并给它赋一个变量的时候,这个变量仅仅参考那个对象,而不是表示这个对象本身!也就是说,变量名指向你计算机中存储那个对象的内存。这被称作名称到对象的绑定。

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', shoplistprint 'mylist is', mylist# notice that both shoplist and mylist both print the same list without# the 'apple' confirming that they point to the same objectprint 'Copy by making a full slice'mylist = shoplist[:] # make a copy by doing a full slicedel mylist[0] # remove first itemprint 'shoplist is', shoplistprint 'mylist is', mylist# notice that now the two lists are different

6、字符串

name = 'Swaroop' # This is a string objectif 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)  //用delimiter来连接mylist的字符

六、面向对象的编程

1、self

Python中的self等价于C++中的self指针和Java、C#中的this参考

2、创建类

class Person:  pass # An empty blockp = Person()print p

3、对象的方法

class Person:  def sayHi(self):    print 'Hello, how are you'p = Person()p.sayHi()

4、初始化

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

5、类与对象的方法

类的变量 由一个类的所有对象(实例)共享使用。只有一个类变量的拷贝,所以当某个对象对类的变量做了改动的时候,这个改动会反映到所有其他的实例上。
对象的变量 由类的每个对象/实例拥有。因此每个对象有自己对这个域的一份拷贝,即它们不是共享的,在同一个类的不同实例中,虽然对象的变量有相同的名称,但是是互不相关的。

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

population属于Person类,因此是一个类的变量。name变量属于对象(它使用self赋值)因此是对象的变量。

6、继承

class SchoolMember:  '''Represents any school member.'''  def __init__(self, name, age):    self.name = nameclass Teacher(SchoolMember):  '''Represents a teacher.'''  def __init__(self, name, age, salary):    SchoolMember.__init__(self, name, age)    self.salary = salary

七、输入输出

1、文件

f = file('poem.txt', 'w') # open for 'w'ritingf.write(poem) # write text to filef.close() # close the filef = file('poem.txt')# if no mode is specified, 'r'ead mode is assumed by defaultwhile True:  line = f.readline()  if len(line) == 0: # Zero length indicates EOF    break  print line,  # Notice comma to avoid automatic newline added by Pythonf.close() # close the file

2、存储器

持久性

import cPickle as p#import pickle as pshoplistfile = 'shoplist.data'# the name of the file where we will store the objectshoplist = ['apple', 'mango', 'carrot']# Write to the filef = file(shoplistfile, 'w')p.dump(shoplist, f) # dump the object to a filef.close()del shoplist # remove the shoplist# Read back from the storagef = file(shoplistfile)storedlist = p.load(f)print storedlist

3、控制台输入

输入字符串 nID = raw_input("Input your id plz")
输入整数 nAge = int(raw_input("input your age plz:\n"))
输入浮点型 fWeight = float(raw_input("input your weight\n"))
输入16进制数据 nHex = int(raw_input('input hex value(like 0x20):\n'),16)
输入8进制数据 nOct = int(raw_input('input oct value(like 020):\n'),8)

八、异常

1、try..except

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

2、引发异常

使用raise语句引发异常。你还得指明错误/异常的名称和伴随异常 触发的 异常对象。你可以引发的错误或异常应该分别是一个Error或Exception类的直接或间接导出类。

class ShortInputException(Exception):  '''A user-defined exception class.'''  def __init__(self, length, atleast):    Exception.__init__(self)    self.length = length    self.atleast = atleastraise ShortInputException(len(s), 3)

3、try..finnally

import timetry:  f = file('poem.txt')  while True: # our usual file-reading idiom    line = f.readline()    if len(line) == 0:      break    time.sleep(2)    print line,finally:  f.close()  print 'Cleaning up...closed the file'

九、Python标准库

1、sys库

sys模块包含系统对应的功能。sys.argv列表,它包含命令行参数。

2、os库

os.name字符串指示你正在使用的平台。比如对于Windows,它是'nt',而对于Linux/Unix用户,它是'posix'。
os.getcwd()函数得到当前工作目录,即当前Python脚本工作的目录路径。
os.getenv()和os.putenv()函数分别用来读取和设置环境变量。
os.listdir()返回指定目录下的所有文件和目录名。
os.remove()函数用来删除一个文件。
os.system()函数用来运行shell命令。
os.linesep字符串给出当前平台使用的行终止符。例如,Windows使用'\r\n',Linux使用'\n'而Mac使用'\r'。
os.path.split()函数返回一个路径的目录名和文件名。
os.path.split('/home/swaroop/byte/code/poem.txt')
('/home/swaroop/byte/code', 'poem.txt')
os.path.isfile()和os.path.isdir()函数分别检验给出的路径是一个文件还是目录。类似地,os.path.existe()函数用来检验给出的路径是否真地存在。

希望本文所述对大家的Python程序设计有所帮助。