介绍
本文方便有经验的程序员进入Python世界.本文适用于python2.5/2.6版本.
Deparecated:Python3 和 python2.x语法不同.如果你正在用python3,请参考新教程:
http://www.cnitblog.com/yunshichen/archive/2009/04/01/55924.html起步走
#! /usr/bin/python
a=2
b=3
c="test"
c=a+b
print "execution result: %i"%c
知识点
- Python是动态语言,变量不须预先声明.
- 打印语句采用C风格
字符串和数字
但有趣的是,在javascript里我们会理想当然的将字符串和数字连接,因为是动态语言嘛.但在Python里有点诡异,如下:
#! /usr/bin/python
a=2
b="test"
c=a+b
运行这行程序会出错,提示你字符串和数字不能连接,于是只好用内置函数进行转换
#! /usr/bin/python
a=2
b="test"
c=str(a)+b
d="1111"
e=a+int(d)
#How to print multiply values
print "c is %s,e is %i" % (c,e)
知识点:
- 用int和str函数将字符串和数字进行转换
- 打印以#开头,而不是习惯的//
- 打印多个参数的方式
国际化
写腻了英文注释,我们要用中文!
#! /usr/bin/python
# -*- coding: utf8 -*-
print "上帝重返人间:马拉多纳出任阿根廷国家足球队主帅."
知识点:
列表
列表类似Javascript的数组,方便易用
#! /usr/bin/python
# -*- coding: utf8 -*-
#定义元组
word=['a','b','c','d','e','f','g']
#如何通过索引访问元组里的元素
a=word[2]
print "a is: "+a
b=word[1:3]
print "b is: "
print b # index 1 and 2 elements of word.
c=word[:2]
print "c is: "
print c # index 0 and 1 elements of word.
d=word[0:]
print "d is: "
print d # All elements of word.
#元组可以合并
e=word[:2]+word[2:]
print "e is: "
print e # All elements of word.
f=word[-1]
print "f is: "
print f # The last elements of word.
g=word[-4:-2]
print "g is: "
print g # index 3 and 4 elements of word.
h=word[-2:]
print "h is: "
print h # The last two elements.
i=word[:-2]
print "i is: "
print i # Everything except the last two characters
l=len(word)
print "Length of word is: "+ str(l)
print "Adds new element"
word.append('h')
print word
#删除元素
del word[0]
print word
del word[1:3]
print word
知识点:
- 列表长度是动态的,可任意添加删除元素.
- 用索引可以很方便访问元素,甚至返回一个子列表
- 更多方法请参考Python的文档
字典
#! /usr/bin/python
x={'a':'aaa','b':'bbb','c':12}
print x['a']
print x['b']
print x['c']
for key in x:
print "Key is %s and value is %s",(key,x[key])
keys=x.items();
print keys[0]
keys[0]='ddd'
print keys[0]
知识点:
字符串
比起C/C++,Python处理字符串的方式实在太让人感动了.把字符串当列表来用吧.
word="abcdefg"
a=word[2]
print "a is: "+a
b=word[1:3]
print "b is: "+b # index 1 and 2 elements of word.
c=word[:2]
print "c is: "+c # index 0 and 1 elements of word.
d=word[0:]
print "d is: "+d # All elements of word.
e=word[:2]+word[2:]
print "e is: "+e # All elements of word.
f=word[-1]
print "f is: "+f # The last elements of word.
g=word[-4:-2]
print "g is: "+g # index 3 and 4 elements of word.
h=word[-2:]
print "h is: "+h # The last two elements.
i=word[:-2]
print "i is: "+i # Everything except the last two characters
l=len(word)
print "Length of word is: "+ str(l)
不过要注意Asc和Unicode字符串的区别:
#! /usr/bin/python
# -*- coding: utf8 -*-
s=raw_input("输入你的中文名,按回车继续
");
print "你的名字是 : " +s;
l=len(s)
print "你中文名字的长度是:"+str(l);
a=unicode(s,"utf8")
l=len(a)
print "对不起,刚才计算错误.我们应该用utf8来计算中文字符串的长度, \
你名字的长度应该是:"+str(l); 知识点:
条件和循环语句
#! /usr/bin/python
x=int(raw_input("Please enter an integer:"))
if x<0:
x=0
print "Negative changed to zero"
elif x==0:
print "Zero"
else:
print "More"
# Loops List
a = ['cat', 'window', 'defenestrate']
for x in a:
print x, len(x)
知识点:
函数
#! /usr/bin/python
# -*- coding: utf8 -*-
def sum(a,b):
return a+b
func = sum
r = func(5,6)
print r
# 提供默认值
def add(a,b=2):
return a+b
r=add(1)
print r
r=add(1,5)
print r
一个好用的函数
#! /usr/bin/python
# -*- coding: utf8 -*-
# The range() function
a =range(5,10)
print a
a = range(-2,-7)
print a
a = range(-7,-2)
print a
a = range(-2,-11,-3) # The 3rd parameter stands for step
print a
知识点:
- Python 不用{}来控制程序结构,他强迫你用缩进来写程序,使代码清晰.
- 定义函数方便简单
- 方便好用的range函数
异常处理
#! /usr/bin/python
s=raw_input("Input your age:")
if s =="":
raise Exception("Input must no be empty.")
try:
i=int(s)
except ValueError:
print "Could not convert data to an integer."
except:
print "Unknown exception!"
else: # It is useful for code that must be executed if the try clause does not raise an exception
print "You are %d" % i," years old"
finally: # Clean up action
print "Goodbye!"