《Python核心编程》第二版第230页第九章练习 Python核心编程答案自己做的

本博客列出的答案不是来自官方资源，是我自己做的练习，可能有误。

9-1.文件过滤。显示一个文件的所有行，忽略以井号（#）开头的行。这个字符被用做Python，Perl，Tcl，等大多数脚本文件的注释符号。附加题：处理不是第一个字符开头的注释。
【答案】
（a）代码如下：

fobj = open('c:\Python Test\P_1.txt')
for eachLine in fobj:
    if eachLine[0] != '#':
        print eachLine,
fobj.close()

文件P_1.txt具体是：
apple
banana
#orange
orange#
orange#orange
pie
donut

【执行结果】
apple
banana
orange#
orange#orange
pie
donut

（b）附加题代码如下：

fobj = open('c:\Python Test\P_1.txt')
for eachLine in fobj:
    switch = True
    for i in eachLine[1:]:
        if i == '#': switch = False
    if switch: print eachLine,
fobj.close()

【执行结果】
apple
banana
#orange
pie
donut

9-2.文件访问。提示输入数字N和文件F，然后显示文件的前N行。
【答案】
代码如下：

N = raw_input("Please input the line numbers: ... ")
F = raw_input("Please input the full location and file name: ... ")
fobj = open(F)
k = fobj.readlines()
for i in k[:int(N)]:
    print i,
fobj.close()

【参考】
http://www.czug.org/python/pyessentialref/09.htm

9-3.文件信息，提示输入一个文件名，然后显示这个文本文件的总行数。
【答案】
代码如下：

filename = raw_input("Please input the file location and name: ... ")
fobj = open(filename)
print len(fobj.readlines())
fobj.close()

***   ***   ***   ***

Example 9.1. os & os.path Modules Example (ospathex.py)

【例子源码】

import os
for tmpdir in ('/tmp', r'c:\Python Test'):
    if os.path.isdir(tmpdir):
        break
else:
    print 'no temp directory available'
    tmpdir = ''
   
if tmpdir:
    os.chdir(tmpdir)
    cwd = os.getcwd()
    print '*** current temporary directory'
    print cwd
    
    print '*** creating example directory...'
    os.mkdir('example')
    os.chdir('example')
    cwd = os.getcwd()
    print '*** new working directory:'
    print cwd
    print '*** original directory listing:'
    print os.listdir(cwd)
    
    print '*** creating test file...'
    fobj = open('test', 'w')
    fobj.write('foo\n')
    fobj.write('bar\n')
    fobj.close()
    print '*** updated directory listing:'
    print os.listdir(cwd)
    
    print "*** renaming 'test' to 'filetest.txt'"
    os.rename('test', 'filetest.txt')
    print '*** updated directory listing:'
    print os.listdir(cwd)
    
    
    path = os.path.join(cwd, os.listdir (cwd)[0])
    print '*** full file pathname'
    print path
    print '*** (pathname, basename) =='
    print os.path.split(path)
    print '*** (filename, extension) =='
    print os.path.splitext(os.path.basename(path))
    
    print '*** displaying file contents:'
    fobj = open(path)
    for eachLine in fobj:
        print eachLine,
    fobj.close()
    
    print '*** deleting test file'
    os.remove(path)
    print '*** updated directory listing:'
    print os.listdir(cwd)
    os.chdir(os.pardir)
    print '*** deleting test directory'
    os.rmdir('example')
    print '*** DONE'

   
【执行结果】
*** current temporary directory
c:\Python Test
*** creating example directory...
*** new working directory:
c:\Python Test\example
*** original directory listing:
[]
*** creating test file...
*** updated directory listing:
['test']
*** renaming 'test' to 'filetest.txt'
*** updated directory listing:
['filetest.txt']
*** full file pathname
c:\Python Test\example\filetest.txt
*** (pathname, basename) ==
('c:\\Python Test\\example', 'filetest.txt')
*** (filename, extension) ==
('filetest', '.txt')
*** displaying file contents:
foo
bar
*** deleting test file
*** updated directory listing:
[]
*** deleting test directory
*** DONE