python内置函数4-file()

Posted 2020-09-01

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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.

| ‘U‘ cannot be combined with ‘w‘ or ‘+‘ mode.

| Methods defined here:

| __delattr__(...)

| x.__delattr__(‘name‘) <==> del x.name

| __enter__(...)

| __enter__() -> self.

| __exit__(...)

| __exit__(*excinfo) -> None. Closes the file.

| __getattribute__(...)

| x.__getattribute__(‘name‘) <==> x.name

| __init__(...)

| x.__init__(...) initializes x; see help(type(x)) for signature

| __iter__(...)

| x.__iter__() <==> iter(x)

| __repr__(...)

| x.__repr__() <==> repr(x)

| __setattr__(...)

| x.__setattr__(‘name‘, value) <==> x.name = value

| close(...)

| close() -> None or (perhaps) an integer. Close the file.

| Sets data attribute .closed to True. A closed file cannot be used for

| further I/O operations. close() may be called more than once without

| error. Some kinds of file objects (for example, opened by popen())

| may return an exit status upon closing.

| fileno(...)

| fileno() -> integer "file descriptor".

| This is needed for lower-level file interfaces, such os.read().

| flush(...)

| flush() -> None. Flush the internal I/O buffer.

| isatty(...)

| isatty() -> true or false. True if the file is connected to a tty device.

| next(...)

| x.next() -> the next value, or raise StopIteration

| read(...)

| read([size]) -> read at most size bytes, returned as a string.

| If the size argument is negative or omitted, read until EOF is reached.

| Notice that when in non-blocking mode, less data than what was requested

| may be returned, even if no size parameter was given.

| readinto(...)

| readinto() -> Undocumented. Don‘t use this; it may go away.

| readline(...)

| readline([size]) -> next line from the file, as a string.

| Retain newline. A non-negative size argument limits the maximum

| number of bytes to return (an incomplete line may be returned then).

| Return an empty string at EOF.

| readlines(...)

| readlines([size]) -> list of strings, each a line from the file.

| Call readline() repeatedly and return a list of the lines so read.

| The optional size argument, if given, is an approximate bound on the

| total number of bytes in the lines returned.

| seek(...)

| seek(offset[, whence]) -> None. Move to new file position.

| Argument offset is a byte count. Optional argument whence defaults to

| 0 (offset from start of file, offset should be >= 0); other values are 1

| (move relative to current position, positive or negative), and 2 (move

| relative to end of file, usually negative, although many platforms allow

| seeking beyond the end of a file). If the file is opened in text mode,

| only offsets returned by tell() are legal. Use of other offsets causes

| undefined behavior.

| Note that not all file objects are seekable.

| tell(...)

| tell() -> current file position, an integer (may be a long integer).

| truncate(...)

| truncate([size]) -> None. Truncate the file to at most size bytes.

| Size defaults to the current file position, as returned by tell().

| write(...)

| write(str) -> None. Write string str to file.

| Note that due to buffering, flush() or close() may be needed before

| the file on disk reflects the data written.

| writelines(...)

| writelines(sequence_of_strings) -> None. Write the strings to the file.

| Note that newlines are not added. The sequence can be any iterable object

| producing strings. This is equivalent to calling write() for each string.

| xreadlines(...)

| xreadlines() -> returns self.

| For backward compatibility. File objects now include the performance

| optimizations previously implemented in the xreadlines module.

| ----------------------------------------------------------------------

| Data descriptors defined here:

| closed

| True if the file is closed

| encoding

| file encoding

| errors

| Unicode error handler

| mode

| file mode (‘r‘, ‘U‘, ‘w‘, ‘a‘, possibly with ‘b‘ or ‘+‘ added)

| name

| file name

| newlines

| end-of-line convention used in this file

| softspace

| flag indicating that a space needs to be printed; used by print

| ----------------------------------------------------------------------

| Data and other attributes defined here:

| __new__ = <built-in method __new__ of type object>

| T.__new__(S, ...) -> a new object with type S, a subtype of T

file(name[, mode[, buffering]])

Constructor function for the file type, described further in section File Objects. The constructor’s arguments are the same as those of the open() built-in function described below.

When opening a file, it’s preferable to use open() instead of invoking this constructor directly. file is more suited to type testing (for example, writing isinstance(f, file)).

中文说明：

读出一个文件的内容。

file()函数是2.2中新增的函数，它与open()函数一样，相当于open()的别名，不过比open()更直观一些。

lines = file(filename).readlines()

for line in lines:

print line

序号方法及描述

1 file.close()

关闭文件。关闭后文件不能再进行读写操作。

2 file.flush()

刷新文件内部缓冲，直接把内部缓冲区的数据立刻写入文件, 而不是被动的等待输出缓冲区写入。

3 file.fileno()