python标准库学习3

wss1051

import operator
sequence = 1, 2, 4
print "add", "=>", reduce(operator.add, sequence)
print "sub", "=>", reduce(operator.sub, sequence)
print "mul", "=>", reduce(operator.mul, sequence)
print "concat", "=>", operator.concat("spam", "egg")
print "repeat", "=>", operator.repeat("spam", 5)
print "getitem", "=>", operator.getitem(sequence, 2)
print "indexOf", "=>", operator.indexOf(sequence, 2)
print "sequenceIncludes", "=>", operator.sequenceIncludes(sequence, 3)

　　add => 7
　　sub => -5
　　mul => 8
　　concat => spamegg
　　repeat => spamspamspamspamspam
　　getitem => 4
　　indexOf => 1
　　sequenceIncludes => False


注意copy中的一些问题：




import copy
a = [[1], [2], [3]]
b = copy.copy( a )
print "before", "=>"
print a
print b
# modify original
a[0][0] = 0
a[1] = None
print "after", "=>"
print a
print b

　　输出的结果是：
　　before =>
　　[[1], [2], [3]]
　　[[1], [2], [3]]
　　after =>
　　[[0], None, [3]]
　　[[0], [2], [3]]
　　测量算法的运行时间：



import time
def procedure():
time.sleep( 2.5 )
# measure process time
t0 = time.clock()
procedure()
print time.clock() - t0, "seconds process time"
# measure wall time
t0 = time.time()
procedure()
print time.time() - t0, "seconds wall time"

　　循环读文本文件：



import fileinput
import sys
for line in fileinput.input( "../src/hello.xml" ):
sys.stdout.write( "-> " )
sys.stdout.write( line )



import fileinput
import glob
import string, sys
for line in fileinput.input( glob.glob( "../src/hello.xml" ) ):
if fileinput.isfirstline(): # first in a file?
sys.stderr.write( "-- reading %s --\n" % fileinput.filename() )
sys.stdout.write( str( fileinput.lineno() ) + " " + string.upper( line ) )

　　复制文件的操作：



import os , shutil
print os.listdir( "../src" )
for file in os.listdir( "../src" ):
if os.path.splitext( file )[1] == ".py":
os.mkdir( "../src/back" )
print file
shutil.copy( file, os.path.join( "back", file ) )


　　可以使用shutil开复制整个目录,然后删除目录



import os , shutil
print os.listdir( ".." )
shutil.copytree("../src", "../src1")
shutil.rmtree( "../src1" )

　　想内存文件写入内容：



import StringIO
file = StringIO.StringIO()
file.write( "This man is no ordinary man. " )
file.write( "This is Mr. F. G. Superman." )
print file.getvalue()

　　使用StringIO模块捕获输出：



import StringIO
import string, sys
stdout = sys.stdout
sys.stdout = file = StringIO.StringIO()
print """a"""
sys.stdout = stdout
print string.upper( file.getvalue() )

　　结果输出A
　　也可以使用cStringIO：



import cStringIO
file = cStringIO.StringIO( "asdaskdgaksdgkasdja" )
print file.getvalue()
print file.read()

　　小技巧：由于cStringIO比StringIO的效率高一点，但是兼容性不行，所以可以使用下面的语句：



try:
import cStringIO
StringIO = cStringIO
except ImportError:
import StringIO
print StringIO

　　类继承的时候构造函数的一点点问题：



class A:
def __init__( self ):
pass
class B( A ):
def __init__( self ):
#A.__init__( self )
super( B, self ).__init__( self )

　　对字典使用“+”法



import UserDict
class Add( UserDict.UserDict ):
def __init__( self, dict = {}, **kwargs ):
UserDict.UserDict.__init__( self )
self.update( dict )
self.update( kwargs )
def __add__( self, other ):
dict = Add( self.data )
dict.update( other )
return dict
a = Add( a = 1 )
b = Add( b = 2 )
print a + b

　　输出的结果为:{'a': 1, 'b': 2}
　　实例类似一个普通的列表对象, 但它允许你通过赋值为列表添加项目.



import UserList
class AutoList( UserList.UserList ):
def __init__( self ):
super( AutoList, self ).__init__( self )
def __setitem__( self, i, item ):
if i == len( self.data ):
self.append( item )
else:
self.data = item
list = AutoList()
for i in range( 10 ):
list = i
print list        

　　输出的结果为：[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
　　随机数：



import random
for i in range(5):
# random float: 0.0