《Python核心編程》第3章 Python基礎 練習

3–10. 異常。

使用類似readTextFile.py 中異常處理的方法取代 readTextFile.py makeTextFile.py 中對os.path.exists() 的調用。反過來， 用os.path.exists() 取代readTextFile.py 中的異常處理方法。

# coding=utf-8
__author__ = 'Ibuki Suika'

'makeTextFile.py -- create text file'

import os
ls = os.linesep

# get filename
fileName = raw_input('filename: ')
while True:
    try:
        f = open(fileName, 'r')
    except IOError:
        break
    else:
        print('ERROR: %s already exists' % fileName)
        fileName = raw_input('filename: ')

# get file content (text) lines
content = []
print "\nEnter lines ('.' by itself to quit).\n"

# loop until user terminates input
while True:
    entry = raw_input('> ')
    if entry == '.':
        break
    else:
        content.append(entry)

# write lines to file with proper line-ending
try:
    fobj = open(fileName, 'w')
except IOError as e:
    print('file open error:%s' % e.message)
else:
    fobj.writelines(['%s%s' % (x, ls) for x in content])
    fobj.close()
print 'DONE!'

# coding=utf-8
__author__ = 'Ibuki Suika'

'readTextFile.py -- read and display text file'

import os

# get filename
fname = raw_input('Enter filename: ')
print

# attempt to open file for reading
if not os.path.exists(fname):
    print "file not exists"
else:
    fobj = open(fname, 'r')
    for eachLine in fobj:
        print eachLine,
    fobj.close()

3–11.字符串格式化

不再抑制readTextFile.py 中 print 語句生成的 NEWLINE 字符，修改你的代碼， 在顯示一行之前刪除每行末尾的空白。這樣， 你就可以移除 print 語句末尾的逗號了。
提示： 使用字符串對象的 strip()方法

# coding=utf-8
__author__ = 'Ibuki Suika'

'readTextFile.py -- read and display text file'

# get filename
fname = raw_input('Enter filename: ')
print

# attempt to open file for reading
try:
    fobj = open(fname, 'r')
except IOError, e:
    print "*** file open error:", e
else:
    for eachLine in fobj:
        print eachLine.strip()
    fobj.close()

3–12. 合併源文件。

將兩段程序合併成一個，給它起一個你喜歡的名字，比方readNwriteTextFiles.py。讓用戶自己選擇是創建還是顯示一個文本文件。

# coding=utf-8
__author__ = 'Ibuki Suika'

import os
ls = os.linesep


def read_text_file():
    fname = raw_input('Enter filename: ')
    print

    try:
        fobj = open(fname, 'r')
    except IOError, e:
        print "*** file open error:", e
    else:
        for eachLine in fobj:
            print eachLine.strip()
        fobj.close()


def write_text_file():
    fileName = raw_input('filename: ')
    while True:
        try:
            f = open(fileName, 'r')
        except IOError:
            break
        else:
            print('ERROR: %s already exists' % fileName)
            fileName = raw_input('filename: ')

    content = []
    print "\nEnter lines ('.' by itself to quit).\n"

    while True:
        entry = raw_input('> ')
        if entry == '.':
            break
        else:
            content.append(entry)

    try:
        fobj = open(fileName, 'w')
    except IOError as e:
        print('file open error:%s' % e.message)
    else:
        fobj.writelines(['%s%s' % (x, ls) for x in content])
        fobj.close()
    print 'DONE!'


def menu():
    print('1. Read File')
    print('2. Write File')
    print('3. Exit')
    choose = input('>')
    return choose

if __name__ == '__main__':
    choose = menu()
    if choose == 1:
        read_text_file()
    elif choose == 2:
        write_text_file()