python基础（内置函数+文件操作+lambda）

一、内置函数

class file(object)
def close(self): # real signature unknown; restored from __doc__
关闭文件
"""
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.
"""

def fileno(self): # real signature unknown; restored from __doc__
文件描述符
"""
fileno() -> integer "file descriptor".

This is needed for lower-level file interfaces, such os.read().
"""
return 0

def flush(self): # real signature unknown; restored from __doc__
刷新文件内部缓冲区
""" flush() -> None.  Flush the internal I/O buffer. """
pass

def isatty(self): # real signature unknown; restored from __doc__
判断文件是否是同意tty设备
""" isatty() -> true or false.  True if the file is connected to a tty device. """
return False

def next(self): # real signature unknown; restored from __doc__
获取下一行数据，不存在，则报错
""" x.next() -> the next value, or raise StopIteration """
pass

def read(self, size=None): # real signature unknown; restored from __doc__
读取指定字节数据
"""
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.
"""
pass

def readinto(self): # real signature unknown; restored from __doc__
读取到缓冲区，不要用，将被遗弃
""" readinto() -> Undocumented.  Don't use this; it may go away. """
pass

def readline(self, size=None): # real signature unknown; restored from __doc__
仅读取一行数据
"""
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.
"""
pass

def readlines(self, size=None): # real signature unknown; restored from __doc__
读取所有数据，并根据换行保存值列表
"""
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.
"""
return []

def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
指定文件中指针位置
"""
seek(offset[, whence]) -> None.  Move to new file position.

Argument offset is a byte count.  Optional argument whence defaults to
(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.
"""
pass

def tell(self): # real signature unknown; restored from __doc__
获取当前指针位置
""" tell() -> current file position, an integer (may be a long integer). """
pass

def truncate(self, size=None): # real signature unknown; restored from __doc__
截断数据，仅保留指定之前数据
"""
truncate([size]) -> None.  Truncate the file to at most size bytes.

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

def write(self, p_str): # real signature unknown; restored from __doc__
写内容
"""
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.
"""
pass

def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
将一个字符串列表写入文件
"""
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.
"""
pass

def xreadlines(self): # real signature unknown; restored from __doc__
可用于逐行读取文件，非全部
"""
xreadlines() -> returns self.

For backward compatibility. File objects now include the performance
optimizations previously implemented in the xreadlines module.
"""
pass

2.x

2.0

a = open("5.log","r+",encoding="utf-8")
# a.truncate()     #依赖于指针，截取数据，只剩下指针所在位置的前面的数据
# a.close()        #关闭
# a.flush()        #强行加入内存
# a.read()         #读
# a.readline()     #只读取第一行
# a.seek(0)        #指针
# a.tell()         #当前指针位置
# a.write()        #写

3、文件上下文管理

为了避免打开文件后忘记关闭，可以通过管理上下文，即：

如此方式，当with代码块执行完毕时，内部会自动关闭并释放文件资源。

在Python 2.7 及以后，with又支持同时对多个文件的上下文进行管理，即：

例：

三、lambda表达式

学习条件运算时，对于简单的 if else 语句，可以使用三元运算来表示，即：

对于简单的函数，也存在一种简便的表示方式，即：lambda表达式