使用 Python 进行稳定可靠的文件操作

1

with

open

(filename) as f:

2

input

=

f.read()

3

output

=

do_something(

input

)

4

with

open

(filename,

'w'

) as f:

5

f.write(output)

1

with

open

(filename,

'r'

) as f:

2

model.read(f)

3

model.process()

4

with

open

(filename,

'w'

) as f:

5

model.write(f)

1

with

open

(filename,

'a+'

) as f:

2

f.seek(

0

)

3

model.

input

(f.read())

4

model.compute()

5

f.seek(

0

)

6

f.truncate()

7

f.write(model.output())

1

withtempfile.NamedTemporaryFile(

2

'w'

,

dir

=

os.path.dirname(filename),delete

=

False

) as tf:

3

tf.write(model.output())

4

tempname

=

tf.name

5

os.rename(tempname,filename)

1

with

open

(filename,

'a'

) as f:

2

f.write(model.output())

1

with

open

(unique_filename(),

'w'

) as f:

2

f.write(model.output())

1

fd

=

os.

open

(filename,os.O_WRONLY | os.O_CREAT| os.O_EXCL,

0o666

)

2

withos.fdopen(fd,

'w'

) as f:

3

f.write(...)

1

with

open

(logfile,

'ab'

) as f:

2

for

i

in

range

(

3

):

3

measure

=

{

'timestamp'

:time.time(),

'value'

:random.random()}

4

record

=

json.dumps(measure).encode()

5

checksum

=

'{:8x}'

.

format

(zlib.crc32(record)).encode()

6

f.write(record

+

b

' '

+

checksum

+

b

'\n'

)

1

$ cat log

2

{

"timestamp"

:

1373396987.258189

,

"value"

:

0.9360123151217828

}

9495b87a

3

{

"timestamp"

:

1373396987.25825

,

"value"

:

0.40429005476999424

}

149afc22

4

{

"timestamp"

:

1373396987.258291

,

"value"

:

0.232021160265939

}d229d937

1

with

open

(logfile,

'rb'

) as f:

2

for

line

in

f:

3

record,checksum

=

line.strip().rsplit(b

' '

,

1

)

4

if

checksum.decode()

=

=

'{:8x}'

.

format

(zlib.crc32(record)):

5

print

(

'read measure:{}'

.

format

(json.loads(record.decode())))

6

else

:

7

print

(

'checksumerror for record{}'

.

format

(record))

1

$ cat log

2

{

"timestamp"

:

1373396987.258189

,

"value"

:

0.9360123151217828

}

9495b87a

3

{

"timestamp"

:

1373396987.25825

,

"value"

:

0.40429005476999424

}

149afc22

4

{

"timestamp"

:

1373396987.258291

,

"value"

:

0.23202

1

$ read_checksummed_log.py log

2

read measure:{

'timestamp'

:

1373396987.258189

,

'value'

:

0.9360123151217828

}

3

read measure:{

'timestamp'

:

1373396987.25825

,

'value'

:

0.40429005476999424

}

4

checksumerror 

for

recordb

'{"timestamp":1373396987.258291,"value":'

1

newfile

=

generate_id()

2

with

open

(newfile

+

'.tmp'

,

'w'

) as f:

3

f.write(model.output())

4

os.rename(newfile

+

'.tmp'

,newfile)

1

with

open

(os.path.join(dirname,

'.lock'

),

'a+'

) as lockfile:

2

fcntl.flock(lockfile,fcntl.LOCK_EX)

3

model.update(dirname)

1

with

open

(os.path.join(dirname,

'.lock'

),

'a+'

) as lockfile:

2

fcntl.flock(lockfile,fcntl.LOCK_SH)

3

model.readall(dirname)

01

mirror

02

|

-

-

483

03

||

-

-

a.tgz

04

||

-

-

b.tgz

05

|`

-

-

index.json

06

|

-

-

484

07

||

-

-

a.tgz

08

||

-

-

b.tgz

09

||

-

-

c.tgz

10

|`

-

-

index.json

11

`

-

-

current

-

>

483

1

def

update():

2

with

open

(filename,

'r+'

) as f:

3

fcntl.flock(f,fcntl.LOCK_EX)

4

n

=

int

(f.read())

5

n

+

=

1

6

f.seek(

0

)

7

f.truncate()

8

f.write(

'{}\n'

.

format

(n))

01

def

update():

02

with

open

(filename) as f:

03

fcntl.flock(f,fcntl.LOCK_EX)

04

n

=

int

(f.read())

05

n

+

=

1

06

withtempfile.NamedTemporaryFile(

07

'w'

,

dir

=

os.path.dirname(filename),delete

=

False

) as tf:

08

tf.write(

'{}\n'

.

format

(n))

09

tempname

=

tf.name

10

os.rename(tempname,filename)

01

class

LockedOpen(

object

):

02

03

def

__init__(

self

,filename,

*

args,

*

*

kwargs):

04

self

.filename

=

filename

05

self

.open_args

=

args

06

self

.open_kwargs

=

kwargs

07

self

.fileobj

=

None

08

09

def

__enter__(

self

):

10

f

=

open

(

self

.filename,

*

self

.open_args,

*

*

self

.open_kwargs)

11

while

True

:

12

fcntl.flock(f,fcntl.LOCK_EX)

13

fnew

=

open

(

self

.filename,

*

self

.open_args,

*

*

self

.open_kwargs)

14

if

os.path.sameopenfile(f.fileno(),fnew.fileno()):

15

fnew.close()

16

break

17

else

:

18

f.close()

19

f

=

fnew

20

self

.fileobj

=

f

21

return

f

22

23

def

__exit__(

self

,_exc_type,_exc_value,_traceback):

24

self

.fileobj.close()

1

def

update(

self

):

2

withLockedOpen(filename,

'r+'

) as f:

3

n

=

int

(f.read())

4

n

+

=

1

5

withtempfile.NamedTemporaryFile(

6

'w'

,

dir

=

os.path.dirname(filename),delete

=

False

) as tf:

7

tf.write(

'{}\n'

.

format

(n))

8

tempname

=

tf.name

9

os.rename(tempname,filename)

1

with

open

(filename,

'w'

) as f:

2

model.write(f)

3

f.flush()

4

os.fdatasync(f)

1

os.rename(tempname,filename)

2

dirfd

=

os.

open

(os.path.dirname(filename),os.O_DIRECTORY)

3

os.fsync(dirfd)

4

os.close(dirfd)