安装完Python之后(我本机的版本是2.5.4),打开IDLE(Python GUI) , 该程序是Python语言解释器,你写的语句能够立即运行.我们写下一句著名的程序语句:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
print
"
Hello,world!
"
并按回车.你就能看到这句被K&R引用的程序世界名言.
在解释器中选择"File"--"New Window" 或快捷键 Ctrl+N , 打开一个新的编辑器.写下如下语句:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
print
"
Hello,world!
"
raw_input( " Press enter key to close this window
"
);
raw_input( " Press enter key to close this window
"
);
保存为a.py文件.按F5,你就可以看到程序的运行结果了.这是Python的第二种运行方式.
找到你保存的a.py文件,双击.也可以看到程序结果.Python的程序能够直接运行,对比Java,这是一个优势.
2.2 国际化支持
我们换一种方式来问候世界.新建一个编辑器并写如下代码:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
print
"
欢迎来到奥运中国!
"
raw_input( " Press enter key to close this window
"
);
raw_input( " Press enter key to close this window
"
);
在你保存代码的时候,Python会提示你是否改变文件的字符集,结果如下:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--># -*- coding: cp936 -*-
print " 欢迎来到奥运中国! "
raw_input( " Press enter key to close this window
"
);
print " 欢迎来到奥运中国! "
raw_input( " Press enter key to close this window
"
);
将该字符集改为我们更熟悉的形式:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--># -*- coding: GBK -*-
print " 欢迎来到奥运中国! " # 使用中文的例子
raw_input( " Press enter key to close this window
"
);
print " 欢迎来到奥运中国! " # 使用中文的例子
raw_input( " Press enter key to close this window
"
);
程序一样运行良好.
2.3 方便易用的计算器
用微软附带的计算器来计数实在太麻烦了.打开Python解释器,直接进行计算:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
a
=
100.0
b = 201.1
c = 2343
print (a + b + c) / c
b = 201.1
c = 2343
print (a + b + c) / c
2.4 字符串,ASCII和UNICODE
可以如下打印出预定义输出格式的字符串:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
print
"""
Usage: thingy [OPTIONS]
- h Display this usage message
- H hostname Hostname to connect to
"""
Usage: thingy [OPTIONS]
- h Display this usage message
- H hostname Hostname to connect to
"""
字符串是怎么访问的?请看这个例子:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
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)
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)
请注意ASCII和UNICODE字符串的区别:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
print
"
Input your Chinese name:
"
s = raw_input( " Press enter to be continued
"
);
print " Your name is :
"
+
s;
l = len(s)
print " Length of your Chinese name in asc codes is: " + str(l);
a = unicode(s, " GBK " )
l = len(a)
print " I'm sorry we should use unicode char!Characters number of your Chinese \
name in unicode is : " +str(l);
s = raw_input( " Press enter to be continued
"
);print " Your name is
:
"
+
s;l = len(s)
print " Length of your Chinese name in asc codes is: " + str(l);
a = unicode(s, " GBK " )
l = len(a)
print " I'm sorry we should use unicode char!Characters number of your Chinese \
name in unicode is : " +str(l);
2.5 使用List
类似Java里的List,这是一种方便易用的数据类型:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
word
=
[
'
a
'
,
'
b
'
,
'
c
'
,
'
d
'
,
'
e
'
,
'
f
'
,
'
g
'
]
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.
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
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.
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
2.6 条件和循环语句
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
# Multi
-
way decision
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)
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)
2.7 如何定义函数
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
# Define and invoke function.
def sum(a,b):
return a + b
func = sum
r = func( 5 , 6 )
print r
# Defines function with default argument
def add(a,b = 2 ):
return a + b
r = add( 1 )
print r
r = add( 1 , 5 )
print r
def sum(a,b):
return a + b
func = sum
r = func( 5 , 6 )
print r
# Defines function with default argument
def add(a,b = 2 ):
return a + b
r = add( 1 )
print r
r = add( 1 , 5 )
print r
并且,介绍一个方便好用的函数:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
# 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
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
2.8 文件I/O
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
spath
=
"
D:/download/baa.txt
"
f = open(spath, " w " ) # Opens file for writing.Creates this file doesn ' t exist.
f.write( " First line 1.\n " )
f.writelines( " First line 2. " )
f.close()
f = open(spath, " r " ) # Opens file for reading
for line in f:
print line
f.close()
f = open(spath, " w " ) # Opens file for writing.Creates this file doesn ' t exist.
f.write( " First line 1.\n " )
f.writelines( " First line 2. " )
f.close()
f = open(spath, " r " ) # Opens file for reading
for line in f:
print line
f.close()
2.9 异常处理
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
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! "
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! "
2.10 类和继承
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
class
Base:
def __init__(self):
self.data = []
def add(self, x):
self.data.append(x)
def addtwice(self, x):
self.add(x)
self.add(x)
# Child extends Base
class Child(Base):
def plus(self,a,b):
return a + b
oChild = Child()
oChild.add( " str1 " )
print oChild.data
print oChild.plus( 2 , 3 )
def __init__(self):
self.data = []
def add(self, x):
self.data.append(x)
def addtwice(self, x):
self.add(x)
self.add(x)
# Child extends Base
class Child(Base):
def plus(self,a,b):
return a + b
oChild = Child()
oChild.add( " str1 " )
print oChild.data
print oChild.plus( 2 , 3 )
2.11 包机制
每一个.py文件称为一个module,module之间可以互相导入.请参看以下例子:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
# a.py
def add_func(a,b):
return a + b
def add_func(a,b):
return a + b
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
# b.py
from a import add_func # Also can be : import a
print " Import add_func from module a "
print " Result of 1 plus 2 is: "
print add_func( 1 , 2 ) # If using " import a " , then here should be " a.add_func "
from a import add_func # Also can be : import a
print " Import add_func from module a "
print " Result of 1 plus 2 is: "
print add_func( 1 , 2 ) # If using " import a " , then here should be " a.add_func "
module可以定义在包里面.Python定义包的方式稍微有点古怪,假设我们有一个parent文件夹,该文件夹有一个child子文件夹.child中有一个module a.py . 如何让Python知道这个文件层次结构?很简单,每个目录都放一个名为_init_.py 的文件.该文件内容可以为空.这个层次结构如下所示:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
parent
-- __init_.py
-- child
-- __init_.py
-- a.py
b.py
-- __init_.py
-- child
-- __init_.py
-- a.py
b.py
那么Python如何找到我们定义的module?在标准包sys中,path属性记录了Python的包路径.你可以将之打印出来:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
import sys
print sys.path
print sys.path
通常我们可以将module的包路径放到环境变量PYTHONPATH中,该环境变量会自动添加到sys.path属性.另一种方便的方法是编程中直接指定我们的module路径到sys.path 中:
<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>-->
import sys
sys.path.append( ' D:\\download ' )
from parent.child.a import add_func
print sys.path
print " Import add_func from module a "
print " Result of 1 plus 2 is: "
print add_func( 1 , 2 )
sys.path.append( ' D:\\download ' )
from parent.child.a import add_func
print sys.path
print " Import add_func from module a "
print " Result of 1 plus 2 is: "
print add_func( 1 , 2 )