首先，我们通过指明我们希望打开的文件和模式来创建一个file类的实例。模式可以为读模式

（'r'）、写模式（'w'）或追加模式（'a'）。事实上还有多得多的模式可以使用，你可以使用

help(file)来了解它们的详情。

f = file('poem.txt', 'w') # open for 'w'riting

f.write(poem) # write text to file

f.close() # close the file

摘一段Python官方指导书原文：

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. The preferred way

| to open a file is with the builtin open() function.

| 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.

|