Python中的file和open用法详解
file和open有什么区别？
file是一个类，而用open函数打开后是返回一个file对象。
file1 = file("aa.txt")
file2 = open("aa.txt")#这个时候返回的是跟file1一样的对象，都可以对aa.txt进行读取，修改。
暂时发现貌似没多大区别，习惯上喜欢用open。
Python 2 里基本没区别。Python 3 里没 file。
Python 2 里，file 是文件对象。open 是返回新创建的文件对象的内建函数，相当于：
def open(*args, **kwargs):
return file(*args, **kwargs)
它真实的定义是：
static PyObject *
builtin_open(PyObject *self, PyObject *args, PyObject *kwds)
{
return PyObject_Call((PyObject*)&PyFile_Type, args, kwds);
}
所以 file 也是能够创建文件的。
file和open用法
help(file) help(open)
老规矩先看一下内置的帮助文档怎么描述file和open，毕竟官方文档是最直接最准确的描述。
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. 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.
简单来说就是file是一个类，使用 file('file_name', 'r+') 这种方式打开文件，返回一个file对象，以写模式打开文件不存在则会被创建。但是更推荐使用内置函数open()来打开一个文件，所以我们再看一下open()的介绍：
Help on built-in function open in module __builtin__:
open(...)
open(name[, mode[, buffering]]) -> file object
Open a file using the file() type, returns a file object. This is the
preferred way to open a file. See file.__doc__ for further information.
(END)
首先open是内置函数，使用方式是open('file_name', mode, buffering)，返回值也是一个file对象，同样，以写模式打开文件如果不存在也会被创建一个新的。
使用实例
In [8]: f1 = open('test.py')
In [9]: f1.
f1.close f1.fileno f1.name f1.readinto f1.softspace f1.writelines
f1.closed f1.flush f1.newlines f1.readline f1.tell f1.xreadlines
f1.encoding f1.isatty f1.next f1.readlines f1.truncate
f1.errors f1.mode f1.read f1.seek f1.write
In [9]: f1.rea
f1.read f1.readinto f1.readline f1.readlines
In [9]: f1.readli
f1.readline f1.readlines
In [9]: f1.readlines()
Out[9]:
['import logging\n',
'\n',
"logging.basicConfig(filename='test.log', level=logging.INFO)\n",
"logging.info('Started')\n",
"print 'x' + 1\n",
"logging.info('Finished')\n"]
In [10]: f1.cl
f1.close f1.closed
In [10]: f1.close()
In [11]: f2 = file('test.py')
In [12]: f2.
f2.close f2.fileno f2.name f2.readinto f2.softspace f2.writelines
f2.closed f2.flush f2.newlines f2.readline f2.tell f2.xreadlines
f2.encoding f2.isatty f2.next f2.readlines f2.truncate
f2.errors f2.mode f2.read f2.seek f2.write
In [12]: f2.read
f2.read f2.readinto f2.readline f2.readlines
In [12]: f2.readli
f2.readline f2.readlines
In [12]: f2.readlines()
Out[12]:
['import logging\n',
'\n',
"logging.basicConfig(filename='test.log', level=logging.INFO)\n",
"logging.info('Started')\n",
"print 'x' + 1\n",
"logging.info('Finished')\n"]
In [13]: f2.cl
f2.close f2.closed
In [13]: f2.closed()
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
----> 1 f2.closed()
TypeError: 'bool' object is not callable
In [14]: f2.closed
Out[14]: False
In [15]: f2.close()
# 打开不存在的文件
In [18]: f3 = file('txt.txt', 'r+')
---------------------------------------------------------------------------
IOError Traceback (most recent call last)
----> 1 f3 = file('txt.txt', 'r+')
IOError: [Errno 2] No such file or directory: 'txt.txt'
In [19]: f3 = file('txt.txt', 'w+')
可以看出来使用的时候区别也不大，不过注意Py3中已经没有了file～这可能也是推荐使用open的一个很重要的原因吧
