1,linux文件知識(shí)補(bǔ)充
~$
ls
-all
drwxr-xr-x 2 qiaozan qiaozan 4096 8月 6 21:21 Templates
-rw-r--r-- 1 qiaozan qiaozan 0 9月 17 07:53 test.txt
解讀:
d和-分別代表目錄和普通文件。
rwxr-xr-x分別代表"(用戶/用戶組/其它用戶)“的”(可讀/可寫(xiě)/可執(zhí)行)"權(quán)限。
可以使用chmod修改文件權(quán)限。
如:linux中給一個(gè)文件加可執(zhí)行權(quán)限:**
chmod +x 文件
或用0~7的數(shù)字
chmod 777 文件
不行加sudo
2,python文件的打開(kāi)方式:
open([文件路徑]文件名,[讀/寫(xiě)/追加/以二進(jìn)制形式等文件打開(kāi)mode],[encoding="UTF-8"])
返回一個(gè)文件對(duì)象
注意:
以二進(jìn)制形式打開(kāi)文件進(jìn)行讀寫(xiě)是對(duì)所有文件通用的
。
如:open([文件路徑]文件名,“rb”)
文件的打開(kāi)模式mode(注意不同的打開(kāi)模式有不同的操作權(quán)限,如以只讀“r”的方式打開(kāi)就不能有寫(xiě)等其它操作,mode之間可以疊加,寫(xiě)在一起就行,但要注意mode不能出現(xiàn)"wr"等模式,如果要同時(shí)讀寫(xiě)需要加“+”號(hào),在這種情況下,讀寫(xiě)共享一個(gè)文件指針,所以要格外注意),注意每次操作完后最好立即關(guān)閉,下次再操作再打開(kāi)就好了:
3,python讀取方式:**
test.txt文件內(nèi)容如下:
第1行 123456789
第2行 123456789
第3行 123456789
第4行 123456789
第5行 123456789
第6行 123456789
第7行 123456789
第8行 123456789
1),read([size]):讀取文件,size可選,若沒(méi)有指定size默認(rèn)為讀取文件的全部,指定size則每次讀取size個(gè)字節(jié)bytes,文件指針后移size個(gè)字節(jié),若文件剩余的不足size個(gè)字節(jié),則返回剩余的字節(jié),下同 。
f
=
open
(
"test.txt"
,
"rb"
)
res
=
f
.
read
(
)
print
(
res
)
結(jié)果:
第
1
行
123456789
第
2
行
123456789
第
3
行
123456789
第
4
行
123456789
第
5
行
123456789
第
6
行
123456789
第
7
行
123456789
第
8
行
123456789
[
Finished
in
0.
2s
]
指定size:
f
=
open
(
"test.txt"
,
"r"
,
encoding
=
"UTF-8"
)
res
=
f
.
read
(
4
)
#第1行
print
(
res
)
若文件剩余的沒(méi)有size個(gè)字節(jié),則返回剩余的字節(jié):
f
=
open
(
"test.txt"
,
"r"
,
encoding
=
"UTF-8"
)
res
=
f
.
read
(
1000
)
print
(
res
)
結(jié)果:
第
1
行
123456789
第
2
行
123456789
第
3
行
123456789
第
4
行
123456789
第
5
行
123456789
第
6
行
123456789
第
7
行
123456789
第
8
行
123456789
[
Finished
in
0.
1s
]
2),readline([size]):讀取一行,size可選,size是對(duì)一行中的讀取字節(jié)數(shù)進(jìn)行限制,若一行中沒(méi)有size個(gè)字節(jié),則返回完整的一行
f
=
open
(
"test.txt"
,
"r"
,
encoding
=
"UTF-8"
)
res
=
f
.
readline
(
)
print
(
res
)
結(jié)果:
第
1
行
123456789
[
Finished
in
0.
1s
]
指定size:
f
=
open
(
"test.txt"
,
"r"
,
encoding
=
"UTF-8"
)
res
=
f
.
readline
(
4
)
#第1行
res
=
f
.
readline
(
400
)
#第1行 123456789
print
(
res
)
3),readlines([size]):讀取整個(gè)文件,并返回文件所有行組成的列表。size可選
f
=
open
(
"test.txt"
,
"r"
,
encoding
=
"UTF-8"
)
res
=
f
.
readlines
(
)
print
(
res
)
結(jié)果返回是列表:
[
'第1行 123456789\n'
,
'第2行 123456789\n'
,
'第3行 123456789\n'
,
'第4行 123456789\n'
,
'第5行 123456789\n'
,
'第6行 123456789\n'
,
'第7行 123456789\n'
,
'第8行 123456789\n'
]
[
Finished
in
0.
1s
]
指定size時(shí),:
f
=
open
(
"test.txt"
,
"r"
,
encoding
=
"UTF-8"
)
# res = f.readlines(3) # ['第1行 123456789\n']
# res = f.readlines(10) # ['第1行 123456789\n']
# res = f.readlines(20) #['第1行 123456789\n', '第2行 123456789\n']
res
=
f
.
readlines
(
30
)
# ['第1行 123456789\n', '第2行 123456789\n', '第3行 123456789\n']
print
(
res
)
4,python文件寫(xiě)入方式:
1)write(str) -> None.:將字符串寫(xiě)入文件
函數(shù)原型:
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.
2)writelines(sequence_of_strings) -> None.寫(xiě)入多行到文件
函數(shù)原型:
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.
5,tell() 和seek的用法演示
f
=
open
(
"test.txt"
,
"r+"
,
encoding
=
"UTF-8"
)
# test.txt文件為空文件
res
=
f
.
write
(
"hello!"
)
print
(
f
.
tell
(
)
)
# 6 寫(xiě)之后文件指針處于第六個(gè)字節(jié)處,也就是文件末尾EOF
res
=
f
.
read
(
)
# 此時(shí)讀什么也讀不到,因文件指針處于文件末尾EOF
print
(
f
.
tell
(
)
)
# 6
f
.
seek
(
0
,
0
)
# seek(偏移量,基準(zhǔn)whence),whence取值(0代表文件開(kāi)頭,1代表當(dāng)前,2代表文件末尾),此處將文件指針重定位到文件開(kāi)頭,偏移量為0的位置
print
(
f
.
tell
(
)
)
# 0 可見(jiàn)已經(jīng)定位到開(kāi)頭了。
res
=
f
.
read
(
)
# hello!
print
(
res
)
6,文件的讀寫(xiě)存在緩存機(jī)制
文件的讀寫(xiě)存在緩存機(jī)制,當(dāng)緩存滿了或者文件刷新(使用 flush強(qiáng)制刷新 /程序正常運(yùn)行結(jié)束/文件被close)都會(huì)導(dǎo)致實(shí)際的IO操作. 當(dāng)你在一次打開(kāi)多次寫(xiě)操作時(shí)就要注意考慮及時(shí)進(jìn)行flush了,否則程序的異常終止會(huì)導(dǎo)致緩存中的數(shù)據(jù)丟失!
7,推薦結(jié)合with語(yǔ)句打開(kāi)文件
with
open
(
'filename'
,
method
=
''
)
as
file_object
:
content
=
file_object
.
read
(
)
特點(diǎn)
1. with語(yǔ)句打開(kāi)文件,并指示了一個(gè)語(yǔ)句塊(即接下來(lái)有一個(gè)縮進(jìn)的多行代碼區(qū)域),該語(yǔ)句塊內(nèi)的代碼是對(duì)文件的
操作,當(dāng)脫離該語(yǔ)句塊時(shí)(即沒(méi)有了縮進(jìn)),則表示with語(yǔ)句塊結(jié)束,接下來(lái)的代碼不是對(duì)文件的操作代碼。
2. 注意,當(dāng)脫離with語(yǔ)句塊的時(shí)候,即表示結(jié)束了文件的操作,這是python會(huì)自動(dòng)調(diào)用 close() 關(guān)閉這個(gè)文件,
此后不能再引用這個(gè)文件對(duì)象。
優(yōu)點(diǎn)
1.使用簡(jiǎn)單方便。
2.自動(dòng)管理文件對(duì)象,不必使用 close()
3.當(dāng)遭遇程序bug時(shí)導(dǎo)致本來(lái)應(yīng)有的 close() 未能執(zhí)行,如果使用with,python保證即使出現(xiàn)故障,也能保證文件被
正確關(guān)閉
python file對(duì)象的所有方法如下:
|
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.
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