mmap
— Memory-mapped file support¶
Availability: not Emscripten, not WASI.
Este módulo não funciona ou não está disponível em plataformas WebAssembly wasm32-emscripten
e wasm32-wasi
. Veja Plataformas WebAssembly para mais informações.
Objetos arquivo mapeados na memória se comportam como bytearray
e como objetos arquivo. Você pode usar objetos mmap na maioria dos lugares onde bytearray
é esperado; por exemplo, você pode usar o módulo re
para pesquisar um arquivo mapeado na memória. Você também pode alterar um único byte executando obj[index] = 97
ou alterar uma subsequência atribuindo a uma fatia: obj[i1:i2] = b'...'
. Você também pode ler e gravar dados começando na posição atual do arquivo e seek()
através do arquivo para diferentes posições.
A memory-mapped file is created by the mmap
constructor, which is
different on Unix and on Windows. In either case you must provide a file
descriptor for a file opened for update. If you wish to map an existing Python
file object, use its fileno()
method to obtain the correct value for the
fileno parameter. Otherwise, you can open the file using the
os.open()
function, which returns a file descriptor directly (the file
still needs to be closed when done).
Nota
Se você deseja criar um mapeamento de memória para um arquivo gravável e armazenado em buffer, deve usar flush()
no arquivo primeiro. Isso é necessário para garantir que as modificações locais nos buffers estejam realmente disponíveis para o mapeamento.
Para as versões Unix e Windows do construtor, access pode ser especificado como um parâmetro opcional de palavra-chave. access aceita um dos quatro valores: ACCESS_READ
, ACCESS_WRITE
ou ACCESS_COPY
para especificar memória somente leitura, gravação ou cópia na gravação, respectivamente ACCESS_DEFAULT
para adiar para prot. access pode ser usado no Unix e no Windows. Se access não for especificado, o mmap do Windows retornará um mapeamento de gravação. Os valores iniciais da memória para todos os três tipos de acesso são obtidos do arquivo especificado. A atribuição a um mapa de memória ACCESS_READ
gera uma exceção TypeError
. A atribuição a um mapa de memória ACCESS_WRITE
afeta a memória e o arquivo subjacente. A atribuição a um mapa de memória ACCESS_COPY
afeta a memória, mas não atualiza o arquivo subjacente.
Alterado na versão 3.7: Adicionada a constante ACCESS_DEFAULT
.
Para mapear a memória anônima, -1 deve ser passado como o fileno junto com o comprimento.
- class mmap.mmap(fileno, length, tagname=None, access=ACCESS_DEFAULT[, offset])¶
(Versão Windows) Mapeia length bytes do arquivo especificado pelo identificador de arquivo fileno e cria um objeto mmap. Se length for maior que o tamanho atual do arquivo, o arquivo será estendido para conter length bytes. Se length for
0
, o tamanho máximo do mapa será o tamanho atual do arquivo, exceto que, se o arquivo estiver vazio, o Windows levantará uma exceção (você não poderá criar um mapeamento vazio no Windows).tagname, if specified and not
None
, is a string giving a tag name for the mapping. Windows allows you to have many different mappings against the same file. If you specify the name of an existing tag, that tag is opened, otherwise a new tag of this name is created. If this parameter is omitted orNone
, the mapping is created without a name. Avoiding the use of the tagname parameter will assist in keeping your code portable between Unix and Windows.offset may be specified as a non-negative integer offset. mmap references will be relative to the offset from the beginning of the file. offset defaults to 0. offset must be a multiple of the
ALLOCATIONGRANULARITY
.Levanta um evento de auditoria
mmap.__new__
com os argumentosfileno
,length
,access
,offset
.
- class mmap.mmap(fileno, length, flags=MAP_SHARED, prot=PROT_WRITE|PROT_READ, access=ACCESS_DEFAULT[, offset])
(Unix version) Maps length bytes from the file specified by the file descriptor fileno, and returns a mmap object. If length is
0
, the maximum length of the map will be the current size of the file whenmmap
is called.flags specifies the nature of the mapping.
MAP_PRIVATE
creates a private copy-on-write mapping, so changes to the contents of the mmap object will be private to this process, andMAP_SHARED
creates a mapping that’s shared with all other processes mapping the same areas of the file. The default value isMAP_SHARED
. Some systems have additional possible flags with the full list specified in MAP_* constants.prot, if specified, gives the desired memory protection; the two most useful values are
PROT_READ
andPROT_WRITE
, to specify that the pages may be read or written. prot defaults toPROT_READ | PROT_WRITE
.access may be specified in lieu of flags and prot as an optional keyword parameter. It is an error to specify both flags, prot and access. See the description of access above for information on how to use this parameter.
offset may be specified as a non-negative integer offset. mmap references will be relative to the offset from the beginning of the file. offset defaults to 0. offset must be a multiple of
ALLOCATIONGRANULARITY
which is equal toPAGESIZE
on Unix systems.To ensure validity of the created memory mapping the file specified by the descriptor fileno is internally automatically synchronized with the physical backing store on macOS.
This example shows a simple way of using
mmap
:import mmap # write a simple example file with open("hello.txt", "wb") as f: f.write(b"Hello Python!\n") with open("hello.txt", "r+b") as f: # memory-map the file, size 0 means whole file mm = mmap.mmap(f.fileno(), 0) # read content via standard file methods print(mm.readline()) # prints b"Hello Python!\n" # read content via slice notation print(mm[:5]) # prints b"Hello" # update content using slice notation; # note that new content must have same size mm[6:] = b" world!\n" # ... and read again using standard file methods mm.seek(0) print(mm.readline()) # prints b"Hello world!\n" # close the map mm.close()
mmap
can also be used as a context manager in awith
statement:import mmap with mmap.mmap(-1, 13) as mm: mm.write(b"Hello world!")
Adicionado na versão 3.2: Suporte a gerenciador de contexto.
The next example demonstrates how to create an anonymous map and exchange data between the parent and child processes:
import mmap import os mm = mmap.mmap(-1, 13) mm.write(b"Hello world!") pid = os.fork() if pid == 0: # In a child process mm.seek(0) print(mm.readline()) mm.close()
Levanta um evento de auditoria
mmap.__new__
com os argumentosfileno
,length
,access
,offset
.Memory-mapped file objects support the following methods:
- close()¶
Closes the mmap. Subsequent calls to other methods of the object will result in a ValueError exception being raised. This will not close the open file.
- closed¶
True
if the file is closed.Adicionado na versão 3.2.
- find(sub[, start[, end]])¶
Returns the lowest index in the object where the subsequence sub is found, such that sub is contained in the range [start, end]. Optional arguments start and end are interpreted as in slice notation. Returns
-1
on failure.Alterado na versão 3.5: Writable bytes-like object is now accepted.
- flush([offset[, size]])¶
Flushes changes made to the in-memory copy of a file back to disk. Without use of this call there is no guarantee that changes are written back before the object is destroyed. If offset and size are specified, only changes to the given range of bytes will be flushed to disk; otherwise, the whole extent of the mapping is flushed. offset must be a multiple of the
PAGESIZE
orALLOCATIONGRANULARITY
.None
is returned to indicate success. An exception is raised when the call failed.Alterado na versão 3.8: Previously, a nonzero value was returned on success; zero was returned on error under Windows. A zero value was returned on success; an exception was raised on error under Unix.
- madvise(option[, start[, length]])¶
Send advice option to the kernel about the memory region beginning at start and extending length bytes. option must be one of the MADV_* constants available on the system. If start and length are omitted, the entire mapping is spanned. On some systems (including Linux), start must be a multiple of the
PAGESIZE
.Availability: Systems with the
madvise()
system call.Adicionado na versão 3.8.
- move(dest, src, count)¶
Copy the count bytes starting at offset src to the destination index dest. If the mmap was created with
ACCESS_READ
, then calls to move will raise aTypeError
exception.
- read([n])¶
Return a
bytes
containing up to n bytes starting from the current file position. If the argument is omitted,None
or negative, return all bytes from the current file position to the end of the mapping. The file position is updated to point after the bytes that were returned.Alterado na versão 3.3: Argument can be omitted or
None
.
- read_byte()¶
Returns a byte at the current file position as an integer, and advances the file position by 1.
- readline()¶
Returns a single line, starting at the current file position and up to the next newline. The file position is updated to point after the bytes that were returned.
- resize(newsize)¶
Resizes the map and the underlying file, if any. If the mmap was created with
ACCESS_READ
orACCESS_COPY
, resizing the map will raise aTypeError
exception.On Windows: Resizing the map will raise an
OSError
if there are other maps against the same named file. Resizing an anonymous map (ie against the pagefile) will silently create a new map with the original data copied over up to the length of the new size.Alterado na versão 3.11: Correctly fails if attempting to resize when another map is held Allows resize against an anonymous map on Windows
- rfind(sub[, start[, end]])¶
Returns the highest index in the object where the subsequence sub is found, such that sub is contained in the range [start, end]. Optional arguments start and end are interpreted as in slice notation. Returns
-1
on failure.Alterado na versão 3.5: Writable bytes-like object is now accepted.
- seek(pos[, whence])¶
Set the file’s current position. whence argument is optional and defaults to
os.SEEK_SET
or0
(absolute file positioning); other values areos.SEEK_CUR
or1
(seek relative to the current position) andos.SEEK_END
or2
(seek relative to the file’s end).
- size()¶
Return the length of the file, which can be larger than the size of the memory-mapped area.
- tell()¶
Returns the current position of the file pointer.
- write(bytes)¶
Write the bytes in bytes into memory at the current position of the file pointer and return the number of bytes written (never less than
len(bytes)
, since if the write fails, aValueError
will be raised). The file position is updated to point after the bytes that were written. If the mmap was created withACCESS_READ
, then writing to it will raise aTypeError
exception.Alterado na versão 3.5: Writable bytes-like object is now accepted.
Alterado na versão 3.6: The number of bytes written is now returned.
Constantes MADV_*¶
- mmap.MADV_NORMAL¶
- mmap.MADV_RANDOM¶
- mmap.MADV_SEQUENTIAL¶
- mmap.MADV_WILLNEED¶
- mmap.MADV_DONTNEED¶
- mmap.MADV_REMOVE¶
- mmap.MADV_DONTFORK¶
- mmap.MADV_DOFORK¶
- mmap.MADV_HWPOISON¶
- mmap.MADV_MERGEABLE¶
- mmap.MADV_UNMERGEABLE¶
- mmap.MADV_SOFT_OFFLINE¶
- mmap.MADV_HUGEPAGE¶
- mmap.MADV_NOHUGEPAGE¶
- mmap.MADV_DONTDUMP¶
- mmap.MADV_DODUMP¶
- mmap.MADV_FREE¶
- mmap.MADV_NOSYNC¶
- mmap.MADV_AUTOSYNC¶
- mmap.MADV_NOCORE¶
- mmap.MADV_CORE¶
- mmap.MADV_PROTECT¶
- mmap.MADV_FREE_REUSABLE¶
- mmap.MADV_FREE_REUSE¶
These options can be passed to
mmap.madvise()
. Not every option will be present on every system.Availability: Systems with the madvise() system call.
Adicionado na versão 3.8.
Constantes MAP_*¶
- mmap.MAP_SHARED¶
- mmap.MAP_PRIVATE¶
- mmap.MAP_DENYWRITE¶
- mmap.MAP_EXECUTABLE¶
- mmap.MAP_ANON¶
- mmap.MAP_ANONYMOUS¶
- mmap.MAP_POPULATE¶
- mmap.MAP_STACK¶
- mmap.MAP_ALIGNED_SUPER¶
- mmap.MAP_CONCEAL¶
These are the various flags that can be passed to
mmap.mmap()
.MAP_ALIGNED_SUPER
is only available at FreeBSD andMAP_CONCEAL
is only available at OpenBSD. Note that some options might not be present on some systems.Alterado na versão 3.10: Added
MAP_POPULATE
constant.Adicionado na versão 3.11: Added
MAP_STACK
constant.Adicionado na versão 3.12: Added
MAP_ALIGNED_SUPER
constant. AddedMAP_CONCEAL
constant.