利用Python中的输入和输出功能进行读取和写入的教程

> print "Hello World!"
Hello World!
> print "The total value is = $", 40.0*45.50
The total value is = $ 1820.0
> print "The total value = $%6.2f" % (40.0*45.50)
The total value = $1820.00
> myfile = file("testit.txt", 'w')
> print  myfile, "Hello World!"
> print  myfile, "The total value = $%6.2f" % (40.0*45.50)
> myfile.close()

% more testit.txt 
Hello World!
The total value = $1820.00

> help(file)
Help on class file in module __builtin__:
class file(object)
 | file(name[, mode[, buffering]]) -> file object
 | 
 | Open a file. The mode can be 'r', 'w' or 'a' for reading (default),
 | writing or appending. The file will be created if it doesn't exist
 | when opened for writing or appending; it will be truncated when
 | opened for writing. Add a 'b' to the mode for binary files.
 | Add a '+' to the mode to allow simultaneous reading and writing.
 | If the buffering argument is given, 0 means unbuffered, 1 means line
 | buffered, and larger numbers specify the buffer size.
 | Add a 'U' to mode to open the file for input with universal newline
 | support. Any line ending in the input file will be seen as a '\n'
 | in Python. Also, a file so opened gains the attribute 'newlines';
 | the value for this attribute is one of None (no newline read yet),
 | '\r', '\n', '\r\n' or a tuple containing all the newline types seen.
 | 
 | 'U' cannot be combined with 'w' or '+' mode.
 | 
 | Note: open() is an alias for file().
 | 
 | Methods defined here:
...

> myfile = open("testit.txt")
> myfile.read()
'Hello World!\nThe total value = $1820.00\n'
> str = myfile.read()
> print str
> myfile.seek(0)
> str = myfile.read()
> print str
Hello World!
The total value = $1820.00
> str.split()
['Hello', 'World!', 'The', 'total', 'value', '=', '$1820.00']
> str.split('\n')
['Hello World!', 'The total value = $1820.00', '']
> for line in str.split('\n'):
...   print line
... 
Hello World!
The total value = $1820.00
> myfile.close()

> myfile = open("testit.txt")
> for line in myfile.readlines():
...   print line
... 
Hello World!
The total value = $1820.00
> myfile.close()
> for line in open("testit.txt").readlines():
...   print line
... 
Hello World!
The total value = $1820.00
> for line in open("testit.txt"):
...   print line
... 
Hello World!
The total value = $1820.00

> myfile = open("testit.txt")
> myfile.readline()
'Hello World!\n'
> myfile.readline()
'The total value = $1820.00\n'
> myfile.readline()
''
> myfile.seek(0)
> myfile.readline()
'Hello World!\n'
> myfile.tell()
13L
> myfile.readline()
'The total value = $1820.00\n'
> myfile.tell()
40L
> myfile.readline()
''
> myfile.tell()
40L
> myfile.seek(0)
> myfile.read(17)
'Hello World!\nThe '
> myfile.seek(0)
> myfile.readlines(23)
['Hello World!\n', 'The total value = $1820.00\n']
> myfile.close()

> mydata = ['Hello World!', 'The total value = $1820.00']
> myfile = open('testit.txt', 'w')
> for line in mydata:
...   myfile.write(line + '\n')
... 
> myfile.close()
> myfile = open("testit.txt")
> myfile.read()
'Hello World!\nThe total value = $1820.00\n'
> myfile.close()
> myfile = open("testit.txt", "r+")
> for line in mydata:
...   myfile.write(line + '\n')
... 
> myfile.seek(0)
> myfile.read()
'Hello World!\nThe total value = $1820.00\n'
> myfile.close()
> myfile = open("testit.txt", "r+a")
> myfile.read()
'Hello World!\nThe total value = $1820.00\n'
> for line in mydata:
...   myfile.write(line + '\n')
... 
> myfile.seek(0)
> myfile.read()
'Hello World!\nThe total value = $1820.00\nHello World!\nThe total value = $1820.00\n'
> myfile.close()

> myfile = open("testit.txt", "wb")
> for c in range(50, 70):
...   myfile.write(chr(c))
... 
> myfile.close()
> myfile = open("testit.txt")
> myfile.read()
'23456789:;<=>?@ABCDE'
> myfile.close()