文件IO

一、打开和关闭文件

In [1]: help(open)

Help on built-in function open in module io:

open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, clo
sefd=True, opener=None)
Open file and return a stream.  Raise IOError upon failure.

file is either a text or byte string giving the name (and the path
if the file isn't in the current working directory) of the file to
be opened or an integer file descriptor of the file to be
wrapped. (If a file descriptor is given, it is closed when the
returned I/O object is closed, unless closefd is set to False.)
...

In [2]: f = open('./hello.py')

In [3]: f
Out[3]: <_io.TextIOWrapper name='./hello.py' mode='r' encoding='UTF-8'>

In [4]: f.read()
Out[4]: ''

In [5]: f.close()

In [6]: f.read()
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-6-571e9fb02258> in <module>()
----> 1 f.read()

ValueError: I/O operation on closed file.

In [7]:

二、文件对象的操作

In [7]: f = open('./hello.py')

In [8]: f.write('test')           # mode=r  默认权限：只读
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-8-c2c133bc4fec> in <module>()
----> 1 f.write('test')

UnsupportedOperation: not writable

In [9]: f.close()

In [10]: f = open('./hello.py', mode='r')

In [11]: f.write('test')
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-11-c2c133bc4fec> in <module>()
----> 1 f.write('test')

UnsupportedOperation: not writable

In [12]: f.read()
Out[12]: ''

In [13]: f.close()

In [14]:

In [14]: f = open('./hello.py', mode='w')  # mode=w 文件不可读；即使文件打开后不做任何操作，也会清空文件

In [15]: %cat hello.py

In [16]: f.read()
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-16-571e9fb02258> in <module>()
----> 1 f.read()

UnsupportedOperation: not readable         # mode=w 当文件不存在的时候，会创建该文件

In [17]: f.write('aaaaa')
Out[17]: 5

In [18]: f.close()

In [19]: %cat hello.py
aaaaa
In [20]: f = open('./hello.py', mode='w')

In [21]: f.close()

In [22]: %cat hello.py

In [23]:

In [28]: f = open('./hello.py', mode='x')   # 当文件存在的时候， 会报错
---------------------------------------------------------------------------
FileExistsError                           Traceback (most recent call last)
<ipython-input-28-d2f14f50d8d0> in <module>()
----> 1 f = open('./hello.py', mode='x')

FileExistsError: [Errno 17] File exists: './hello.py'

In [29]: %rm hello.py

In [30]: f = open('./hello.py', mode='x')   # 当文件存在的时候， 会报错， 不可读，可写

In [31]: f.read()
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-31-571e9fb02258> in <module>()
----> 1 f.read()

UnsupportedOperation: not readable

In [32]: f.write('abcd')
Out[32]: 4

In [33]: f.close()

In [34]: %cat hello.py
abcd
In [35]:

In [40]: %rm hello.py

In [41]: f = open('./hello.py', mode='a')   # mode=a, 不可读， 可写；并且是追加写

In [42]: f.write('abcd')
Out[42]: 4

In [43]: f.read()
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-43-571e9fb02258> in <module>()
----> 1 f.read()

UnsupportedOperation: not readable

In [44]: f.close()

In [45]: %cat hello.py
abcd
In [46]:

总结：

从 控制读写的模式：

从其他方面来看：

In [46]: f = open('./hello.py', mode='rt')  # mode=t 是以文本方式打开文件

In [47]: s = f.read()

In [48]: s
Out[48]: 'abcd'

In [49]: f.close()

In [50]: f = open('./hello.py', mode='rb')  # mode=b 是以字节方式打开文件

In [51]: s = f.read()

In [52]: s
Out[52]: b'abcd'

In [53]: f.close()

In [54]:

In [55]: f = open('./hello.py', mode='r+')  # mode=r+  可读可写，并且是一个追加写

In [56]: f.read()
Out[56]: 'abcd'

In [57]: f.write('efgh')
Out[57]: 4

In [58]: f.read()
Out[58]: ''

In [59]: f.close()

In [60]: %cat hello.py
abcdefgh
In [61]:

In [62]: f = open('./hello.py', mode='w+')    # mode=w+ 可读可写， 同时会清空文件

In [63]: f.read()
Out[63]: ''

In [64]: f.write('马哥教育')
Out[64]: 4

In [65]: f.close()

In [66]: %cat hello.py
马哥教育
In [67]:

三、文件指针

In [67]: help(f.tell)

Help on built-in function tell:

tell() method of _io.TextIOWrapper instance
Return current stream position.
~   # 返回当前流的位置

(END)

In [69]: f = open('./hello.py')             # mode=rt

In [70]: f.tell()
Out[70]: 0

In [71]: f.read()
Out[71]: '马哥教育'

In [72]: f.tell()
Out[72]: 12

In [73]: f.close()

In [74]: f = open('./hello.py', mode='a')

In [75]: f.tell()
Out[75]: 12

In [76]: f.close()

In [77]:

In [78]: f = open('./hello.py')

In [79]: help(f.seek)

Help on built-in function seek:

seek(cookie, whence=0, /) method of _io.TextIOWrapper instance
Change stream position.

Change the stream position to the given byte offset. The offset is
interpreted relative to the position indicated by whence.  Values
for whence are:
# 偏移量应当为0 或正整数
* 0 -- start of stream (the default); offset should be zero or positive
* 1 -- current stream position; offset may be negative  # 偏移量可以为0或负整数
* 2 -- end of stream; offset is usually negative  # 偏移量 通常为 负整数

Return the new absolute position.
# 返回新的绝对位置
~
(END)

In [91]: f = open('./hello.py', 'w+')

In [92]: f.write('magedu')
Out[92]: 6

In [93]: f.close()

In [94]: %cat hello.py
magedu
In [95]: f = open('./hello.py')

In [96]: f.tell()
Out[96]: 0

In [97]: f.read()
Out[97]: 'magedu'

In [98]: f.tell()
Out[98]: 6

In [99]: f.seek(0, 0)
Out[99]: 0

In [100]: f.tell()
Out[100]: 0

In [101]: f.read()
Out[101]: 'magedu'

In [102]: f.seek(2, 0)
Out[102]: 2

In [103]: f.tell()
Out[103]: 2

In [104]: f.read()
Out[104]: 'gedu'

In [105]: f.seek(0, 0)
Out[105]: 0

In [106]: f.read()
Out[106]: 'magedu'

In [107]: f.seek(4, 1)
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-107-d74820aa25fe> in <module>()
----> 1 f.seek(4, 1)

UnsupportedOperation: can't do nonzero cur-relative seeks

In [108]: f.seek(0, 1)
Out[108]: 6

In [109]: f.seek(0, 2)
Out[109]: 6

In [110]: f.tell()
Out[110]: 6

In [111]: f.close()

In [112]:

总结：

mode=t

In [113]: f = open('./hello.py', mode='w')

In [114]: f.write('马哥教育')
Out[114]: 4

In [115]: f.close()

In [116]: f = open('./hello.py', mode='rb')

In [117]: f.tell()
Out[117]: 0

In [118]: f.seek(3)
Out[118]: 3

In [119]: f.read()
Out[119]: b'\xe5\x93\xa5\xe6\x95\x99\xe8\x82\xb2'

In [120]: f.seek(3)
Out[120]: 3

In [121]: f.read().decode()
Out[121]: '哥教育'

In [122]: f.seek(3)
Out[122]: 3

In [123]: f.seek(3, 1)
Out[123]: 6

In [124]: f.seek(3, 2)
Out[124]: 15

In [125]: f.read()
Out[125]: b''

In [126]: f.read().decode()
Out[126]: ''

In [127]: f.seek(-3, 2)
Out[127]: 9

In [128]: f.read().decode()
Out[128]: '育'

In [129]: f.seek(13)
Out[129]: 13

In [130]: f.seek(-13, 2)
---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
<ipython-input-130-6a41921c313a> in <module>()
----> 1 f.seek(-13, 2)

OSError: [Errno 22] Invalid argument

In [131]:

总结：

mode=b

移动文件指针：

1、落盘操作（flush）

In [132]: f = open('./hello.py', 'wb')

In [133]: f.write(b'abc')
Out[133]: 3

In [134]: %cat hello.py

In [135]: f.flush()          # 落盘

In [136]: %cat hello.py
abc
In [137]: f.write(b'apapapa')
Out[137]: 7

In [138]: %cat hello.py
abc
In [139]: f.close()          # 自带 flush

In [140]: %cat hello.py
abcapapapa
In [141]:

2、buffering（缓冲区）

In [145]: f = open('./hello.py', 'wb', buffering=5)

In [146]: f.write(b'abc')
Out[146]: 3

In [147]: %cat hello.py

In [148]: f.write(b'abc')
Out[148]: 3

In [149]: %cat hello.py
abc
In [150]: f.close()

In [151]: %cat hello.py
abcabc
In [152]: f = open('./hello.py', 'wb', buffering=5)

In [153]: f.write(b'a')
Out[153]: 1

In [154]: f.write(b'b')
Out[154]: 1

In [155]: f.write(b'q')
Out[155]: 1

In [156]: f.write(b'ab')
Out[156]: 2

In [157]: f.write(b'1')
Out[157]: 1

In [158]: %cat hello.py
abqab
In [159]: f.close()

In [160]:

In [161]: f = open('./hello.py', 'wb', buffering=0)

In [162]: f.write(b'a')
Out[162]: 1

In [163]: %cat hello.py
a
In [164]: f.write(b'b')
Out[164]: 1

In [165]: %cat hello.py
ab
In [166]: f.close()

In [167]: f = open('./hello.py', 'wb', buffering=0)

In [168]: f.write(b'abcdefg')
Out[168]: 7

In [169]: %cat hello.py
abcdefg
In [170]:

In [170]: import io

In [171]: io.DEFAULT_BUFFER_SIZE
Out[171]: 8192

In [172]: f = open('./hello.py', 'wt', buffering=1)   # 只有当buffering=1 的时候，才是 line buffer

In [173]: f.write('abc')
Out[173]: 3

In [174]: %cat hello.py

In [175]: f.write('\n')
Out[175]: 1

In [176]: %cat hello.py
abc

In [177]: f.close()

In [185]: f = open('./hello.py', 'wt', buffering=5)

In [186]: f.write('abc')
Out[186]: 3

In [187]: %cat hello.py

In [188]: f.write('\n')
Out[188]: 1

In [189]: %cat hello.py

In [190]: f.write('a' * io.DEFAULT_BUFFER_SIZE)
Out[190]: 8192

In [191]: f.close()

In [192]: f = open('./hello.py', 'wt', buffering=5)

In [193]: f.write('a' * io.DEFAULT_BUFFER_SIZE)
Out[193]: 8192

In [194]: %cat hello.py

In [195]: f.write('b')
Out[195]: 1

In [196]: %cat hello.py
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa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In [197]: f.close()

In [198]:

buffering>1 的时候， 缓冲区的大小为 io.DEFAULT_BUFFER_SIZE； 当缓冲区满时，flush缓冲区连同本次写入的内容一起 落盘。

总结：

In [217]: f = open('hello.py', 'w+', buffering=1)

In [218]: f.write('abcd')
Out[218]: 4

In [219]: f.read()
Out[219]: ''

In [220]: f.seek(0)
Out[220]: 0

In [221]: f.tell()
Out[221]: 0

In [222]: f.read()
Out[222]: 'abcd'

In [223]: f.close()

In [242]: f = open('hello.py', 'w+', buffering=1)

In [243]: f.write('abc')
Out[243]: 3

In [244]: f = open('hello.py', 'r+')

In [245]: f.write('1234\n')
Out[245]: 5

In [246]: f.write('hjhk\n')
Out[246]: 5

In [247]: f.write('op976\n')
Out[247]: 6

In [248]: f.seek(0)
Out[248]: 0

In [249]: f.read(4)       # 跟着指针走
Out[249]: '1234'

In [250]: f.read(4)
Out[250]: '\nhjh'

In [251]: f.read(-1)
Out[251]: 'k\nop976\n'

In [252]: f.seek(0)
Out[252]: 0

In [253]: f.read(0)
Out[253]: ''

In [254]: f.readline()
Out[254]: '1234\n'

In [255]: help(f.readline)

Help on built-in function readline:

readline(size=-1, /) method of _io.TextIOWrapper instance
Read until newline or EOF.

Returns an empty string if EOF is hit immediately.
~

(END)

In [256]: f.seek(0)
Out[256]: 0

In [257]: f.readline(2)
Out[257]: '12'

In [258]: f.readlines()
Out[258]: ['34\n', 'hjhk\n', 'op976\n']

In [259]: f.seek(0)
Out[259]: 0

In [260]: for line in f:
...:     print(line)
...:
1234

hjhk

op976

In [261]: f.writable()
Out[261]: True

In [262]: f.write('bnm\n')
Out[262]: 4

In [263]: f.writelines(['bnm\n', '098765fgh\n'])

In [264]: f.flush()

In [265]: %cat hello.py
1234
hjhk
op976
bnm
bnm
098765fgh

In [266]: f.seekable()
Out[266]: True

In [267]:

2、sys 模块

In [272]: import sys

In [273]: sys.stderr.seekable()     # 进行指针测试
Out[273]: False

In [274]: f.fileno()                # 如果 f 含有文件描述符则返回；如果 f 没有使用文件描述符，则返回osError
Out[274]: 12

In [275]: f.isatty()                # 返回这是否是一个“交互”流 ；如果不能确定，则返回 false
Out[275]: False

In [276]: f.name                    # 返回 f 的名字
Out[276]: 'hello.py'

In [277]: f.buffer                  # 返回缓冲区 信息？
Out[277]: <_io.BufferedRandom name='hello.py'>

In [278]: f.truncate()    # 文件指针保持不变。大小默认为当前IO ；根据据tell()位置，返回新的大小。
Out[278]: 34

In [279]: f.close()

In [322]: f = open('hello.py', 'r+b')

In [323]: f1 = open('test.txt', 'r+b')

In [324]: f1.write(b'lkjhgfdsajytr')
Out[324]: 13

In [325]: f1.close()

In [326]: f.seek(0)
Out[326]: 0

In [327]: f.readinto(f1)    # readinto（缓冲，/）_io.bufferedrandom的实例方法
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-327-d3164cf92344> in <module>()
----> 1 f.readinto(f1)

TypeError: readinto() argument must be read-write bytes-like object, not _io.BufferedRandom
# TypeError：readinto()参数必须是可读写的， 字节的形式的对象，不能够是_io.bufferedrandom
In [328]:

In [328]: f.close()

In [329]: f1.close()

In [330]: f1 = open('test.txt', 'r+b')

In [331]: f = open('hello.py', 'r+b')

In [332]: buffer = bytearray()

In [333]: f.readinto(buffer)
Out[333]: 0

In [334]: f.close()

In [335]: f1.close()

In [336]: