3-1 变量在第一次被赋值时自动声明。在赋值时解释器会根据语法和右侧的操作数来决定新对象的类型。
3-2 函数总是返回一个值，显式 return 的值或者 None。返回的值的类型也是动态确定。
3-3 因为变量名 xxx 对 Python 来说有特殊含义，对于普通的变量应当避免这种命名风格。
3-4 可以，使用 “;”
3-5 可以，使用 “" 或者括号
3-6
(a)x = 1, y = 2, z = 3
(b)z = 2, x = 3, y = 1
3-7 40XL, $aving$, 0x40L, thisIsn’tAVar, big-daddy, 2hot2touch, counter-1 不合法。不是以字母或者下划线开头，或者有非字母下划线数字的字符。print, if 是关键字。
3-10
用异常处理取代对 os.path.exists() 的调用：
import os
ls = os.linesep
while True:
fname = raw_input('input a filename:')
# if os.path.exists(fname):
# print "Error: '%s' already exists" % fname
# else:
# break
try:
fobj = open(fname, 'r')
except IOError, e:
break;
else:
print "Error: '%s' already exists" % fname
fobj.close()
all = []
print "\nEnter lines ('.' by itself to quit).\n"
while True:
entry = raw_input('>')
if entry == '.':
break
else:
all.append(entry)
fobj = open(fname, 'w')
fobj.writelines(['%s%s' % (x, ls) for x in all])
fobj.close()
print 'Done!'
用 os.path.exists() 取代异常处理方法：
import os
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,
# fobj.close()
if os.path.exists(fname):
fobj = open(fname, 'r')
for eachLine in fobj:
print eachLine,
fobj.close()
else:
print 'this file not exists'
3-11
import os
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,
# fobj.close()
if os.path.exists(fname):
fobj = open(fname, 'r')
for eachLine in fobj:
print eachLine.strip()
fobj.close()
else:
print 'this file not exists'
3-12
"""to read or make a file"""
import os
def makeTextFile():
'''make a file'''
ls = os.linesep
while True:
fname = raw_input('input a filename:')
# if os.path.exists(fname):
# print "Error: '%s' already exists" % fname
# else:
# break
try:
fobj = open(fname, 'r')
except IOError, e:
break;
else:
print "Error: '%s' already exists" % fname
fobj.close()
all = []
print "\nEnter lines ('.' by itself to quit).\n"
while True:
entry = raw_input('>')
if entry == '.':
break
else:
all.append(entry)
fobj = open(fname, 'w')
fobj.writelines(['%s%s' % (x, ls) for x in all])
fobj.close()
print 'Done!'
def readTextFile():
'''read a 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,
# fobj.close()
if os.path.exists(fname):
fobj = open(fname, 'r')
for eachLine in fobj:
print eachLine.strip()
fobj.close()
else:
print 'this file not exists'
def main():
'''main menu'''
while True:
print '1.Read a file'
print '2.Make a file'
print 'x.exit'
myStr = raw_input('input your choice:')
if myStr == '1':
readTextFile()
elif myStr == '2':
makeTextFile()
elif myStr == 'x':
break
if __name__ == '__main__':
main()
3-13
Windows 下 curses 模块貌似无法正常使用……
迂回的实现思路是将文件内容按行读取到一个列表里，
然后让用户修改每一行，
最后让用户选择是否保存，
保存则重写文件，
不保存则退出。