python 基础 文件编辑

一、打开文件

open函数，该函数用于文件处理

1、文件句柄  = open(‘文件路径‘, ‘模式‘)

打开文件时，需要指定文件路径和以何等方式打开文件，打开后，即可获取该文件句柄，日后通过此文件句柄对该文件操作。

打开文件的模式有：

• r，只读模式【默认】
• w，只写模式【不可读；不存在则创建；存在则清空内容；】
• x， 只写模式【不可读；不存在则创建，存在则报错】
• a， 追加模式【可读；   不存在则创建；存在则只追加内容；】

‘+’表示可以同时读写某个文件

• r+，读写【可读，可写】
• w+，写读【可读，可写】
• x+ ，写读【可读，可写】
• a+， 写读【可读，可写】

“b"表示以字节的方式操作

• rb或r+b
• wb或w+b
• xb或x+b
• ab或a+b

以b方式打开时，读取到的内容也是字节类型，写入时也需要提供字节类型

二，操作

  1 class file(object)
  2     def close(self): # real signature unknown; restored from __doc__
  3         关闭文件
  4         """
  5         close() -> None or (perhaps) an integer.  Close the file.
  6
  7         Sets data attribute .closed to True.  A closed file cannot be used for
  8         further I/O operations.  close() may be called more than once without
  9         error.  Some kinds of file objects (for example, opened by popen())
 10         may return an exit status upon closing.
 11         """
 12
 13     def fileno(self): # real signature unknown; restored from __doc__
 14         文件描述符
 15          """
 16         fileno() -> integer "file descriptor".
 17
 18         This is needed for lower-level file interfaces, such os.read().
 19         """
 20         return 0
 21
 22     def flush(self): # real signature unknown; restored from __doc__
 23         刷新文件内部缓冲区
 24         """ flush() -> None.  Flush the internal I/O buffer. """
 25         pass
 26
 27
 28     def isatty(self): # real signature unknown; restored from __doc__
 29         判断文件是否是同意tty设备
 30         """ isatty() -> true or false.  True if the file is connected to a tty device. """
 31         return False
 32
 33
 34     def next(self): # real signature unknown; restored from __doc__
 35         获取下一行数据，不存在，则报错
 36         """ x.next() -> the next value, or raise StopIteration """
 37         pass
 38
 39     def read(self, size=None): # real signature unknown; restored from __doc__
 40         读取指定字节数据
 41         """
 42         read([size]) -> read at most size bytes, returned as a string.
 43
 44         If the size argument is negative or omitted, read until EOF is reached.
 45         Notice that when in non-blocking mode, less data than what was requested
 46         may be returned, even if no size parameter was given.
 47         """
 48         pass
 49
 50     def readinto(self): # real signature unknown; restored from __doc__
 51         读取到缓冲区，不要用，将被遗弃
 52         """ readinto() -> Undocumented.  Don‘t use this; it may go away. """
 53         pass
 54
 55     def readline(self, size=None): # real signature unknown; restored from __doc__
 56         仅读取一行数据
 57         """
 58         readline([size]) -> next line from the file, as a string.
 59
 60         Retain newline.  A non-negative size argument limits the maximum
 61         number of bytes to return (an incomplete line may be returned then).
 62         Return an empty string at EOF.
 63         """
 64         pass
 65
 66     def readlines(self, size=None): # real signature unknown; restored from __doc__
 67         读取所有数据，并根据换行保存值列表
 68         """
 69         readlines([size]) -> list of strings, each a line from the file.
 70
 71         Call readline() repeatedly and return a list of the lines so read.
 72         The optional size argument, if given, is an approximate bound on the
 73         total number of bytes in the lines returned.
 74         """
 75         return []
 76
 77     def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
 78         指定文件中指针位置
 79         """
 80         seek(offset[, whence]) -> None.  Move to new file position.
 81
 82         Argument offset is a byte count.  Optional argument whence defaults to
 83 (offset from start of file, offset should be >= 0); other values are 1
 84         (move relative to current position, positive or negative), and 2 (move
 85         relative to end of file, usually negative, although many platforms allow
 86         seeking beyond the end of a file).  If the file is opened in text mode,
 87         only offsets returned by tell() are legal.  Use of other offsets causes
 88         undefined behavior.
 89         Note that not all file objects are seekable.
 90         """
 91         pass
 92
 93     def tell(self): # real signature unknown; restored from __doc__
 94         获取当前指针位置
 95         """ tell() -> current file position, an integer (may be a long integer). """
 96         pass
 97
 98     def truncate(self, size=None): # real signature unknown; restored from __doc__
 99         截断数据，仅保留指定之前数据
100         """
101         truncate([size]) -> None.  Truncate the file to at most size bytes.
102
103         Size defaults to the current file position, as returned by tell().
104         """
105         pass
106
107     def write(self, p_str): # real signature unknown; restored from __doc__
108         写内容
109         """
110         write(str) -> None.  Write string str to file.
111
112         Note that due to buffering, flush() or close() may be needed before
113         the file on disk reflects the data written.
114         """
115         pass
116
117     def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
118         将一个字符串列表写入文件
119         """
120         writelines(sequence_of_strings) -> None.  Write the strings to the file.
121
122         Note that newlines are not added.  The sequence can be any iterable object
123         producing strings. This is equivalent to calling write() for each string.
124         """
125         pass
126
127     def xreadlines(self): # real signature unknown; restored from __doc__
128         可用于逐行读取文件，非全部
129         """
130         xreadlines() -> returns self.
131
132         For backward compatibility. File objects now include the performance
133         optimizations previously implemented in the xreadlines module.
134         """
135         pass

  1 class TextIOWrapper(_TextIOBase):
  2     """
  3     Character and line based layer over a BufferedIOBase object, buffer.
  4
  5     encoding gives the name of the encoding that the stream will be
  6     decoded or encoded with. It defaults to locale.getpreferredencoding(False).
  7
  8     errors determines the strictness of encoding and decoding (see
  9     help(codecs.Codec) or the documentation for codecs.register) and
 10     defaults to "strict".
 11
 12     newline controls how line endings are handled. It can be None, ‘‘,
 13     ‘\n‘, ‘\r‘, and ‘\r\n‘.  It works as follows:
 14
 15     * On input, if newline is None, universal newlines mode is
 16       enabled. Lines in the input can end in ‘\n‘, ‘\r‘, or ‘\r\n‘, and
 17       these are translated into ‘\n‘ before being returned to the
 18       caller. If it is ‘‘, universal newline mode is enabled, but line
 19       endings are returned to the caller untranslated. If it has any of
 20       the other legal values, input lines are only terminated by the given
 21       string, and the line ending is returned to the caller untranslated.
 22
 23     * On output, if newline is None, any ‘\n‘ characters written are
 24       translated to the system default line separator, os.linesep. If
 25       newline is ‘‘ or ‘\n‘, no translation takes place. If newline is any
 26       of the other legal values, any ‘\n‘ characters written are translated
 27       to the given string.
 28
 29     If line_buffering is True, a call to flush is implied when a call to
 30     write contains a newline character.
 31     """
 32     def close(self, *args, **kwargs): # real signature unknown
 33         关闭文件
 34         pass
 35
 36     def fileno(self, *args, **kwargs): # real signature unknown
 37         文件描述符
 38         pass
 39
 40     def flush(self, *args, **kwargs): # real signature unknown
 41         刷新文件内部缓冲区
 42         pass
 43
 44     def isatty(self, *args, **kwargs): # real signature unknown
 45         判断文件是否是同意tty设备
 46         pass
 47
 48     def read(self, *args, **kwargs): # real signature unknown
 49         读取指定字节数据
 50         pass
 51
 52     def readable(self, *args, **kwargs): # real signature unknown
 53         是否可读
 54         pass
 55
 56     def readline(self, *args, **kwargs): # real signature unknown
 57         仅读取一行数据
 58         pass
 59
 60     def seek(self, *args, **kwargs): # real signature unknown
 61         指定文件中指针位置
 62         pass
 63
 64     def seekable(self, *args, **kwargs): # real signature unknown
 65         指针是否可操作
 66         pass
 67
 68     def tell(self, *args, **kwargs): # real signature unknown
 69         获取指针位置
 70         pass
 71
 72     def truncate(self, *args, **kwargs): # real signature unknown
 73         截断数据，仅保留指定之前数据
 74         pass
 75
 76     def writable(self, *args, **kwargs): # real signature unknown
 77         是否可写
 78         pass
 79
 80     def write(self, *args, **kwargs): # real signature unknown
 81         写内容
 82         pass
 83
 84     def __getstate__(self, *args, **kwargs): # real signature unknown
 85         pass
 86
 87     def __init__(self, *args, **kwargs): # real signature unknown
 88         pass
 89
 90     @staticmethod # known case of __new__
 91     def __new__(*args, **kwargs): # real signature unknown
 92         """ Create and return a new object.  See help(type) for accurate signature. """
 93         pass
 94
 95     def __next__(self, *args, **kwargs): # real signature unknown
 96         """ Implement next(self). """
 97         pass
 98
 99     def __repr__(self, *args, **kwargs): # real signature unknown
100         """ Return repr(self). """
101         pass
102
103     buffer = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
104
105     closed = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
106
107     encoding = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
108
109     errors = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
110
111     line_buffering = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
112
113     name = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
114
115     newlines = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
116
117     _CHUNK_SIZE = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
118
119     _finalizing = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
120 复制代码
121 三、管理上下文
122
123 为了避免打开文件后忘记关闭，可以通过管理上下文，即：
124
125 1
126 2
127 3
128 with open(‘log‘,‘r‘) as f:
129
130     ...
131 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。
132
133 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：
134
135 1
136 2
137 with open(‘log1‘) as obj1, open(‘log2‘) as obj2:
138     pass

lambda表达式

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

# 普通条件语句
if 1 == 1:
    name = ‘sunlieqi‘
else:
    name = ‘alex‘

# 三元运算
name = ‘sunlieqi‘ if 1 == 1 else ‘alex‘

对于简单的函数，也存在一种简便的表示方式，即：lambda表达式

# ###################### 普通函数 ######################
# 定义函数（普通方式）
def func(arg):
    return arg + 1

# 执行函数
result = func(123)

# ###################### lambda ######################

# 定义函数（lambda表达式）
my_lambda = lambda arg : arg + 1

# 执行函数
result = my_lambda(112）

递归

利用函数编写如下数列：

斐波那契数列指的是这样一个数列 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233，377，610，987，1597，2584，4181，6765，10946，17711，28657，46368...

def func(arg1,arg2):
    if arg1 == 0:
        print arg1, arg2
    arg3 = arg1 + arg2
    print arg3
    func(arg2, arg3)

func(0,1)