pyarrow.MemoryMappedFile#

class pyarrow.MemoryMappedFile#

Bases: NativeFile

A stream that represents a memory-mapped file.

Supports ‘r’, ‘r+’, ‘w’ modes.

Examples

Create a new file with memory map:

>>> import pyarrow as pa
>>> mmap = pa.create_memory_map('example_mmap.dat', 10)
>>> mmap
<pyarrow.MemoryMappedFile closed=False own_file=False is_seekable=True is_writable=True is_readable=True>
>>> mmap.close()

Open an existing file with memory map:

>>> with pa.memory_map('example_mmap.dat') as mmap:
...     mmap
...
<pyarrow.MemoryMappedFile closed=False own_file=False is_seekable=True is_writable=False is_readable=True>

__init__(*args, **kwargs)#

Methods

`__init__`(args, *kwargs)
`close`(self)
`create`(path, size)	Create a MemoryMappedFile
`download`(self, stream_or_path[, buffer_size])	Read this file completely to a local path or destination stream.
`fileno`(self)
`flush`(self)	Flush the stream, if applicable.
`get_stream`(self, file_offset, nbytes)	Return an input stream that reads a file segment independent of the state of the file.
`isatty`(self)
`metadata`(self)	Return file metadata
`read`(self[, nbytes])	Read and return up to n bytes.
`read1`(self[, nbytes])	Read and return up to n bytes.
`read_at`(self, nbytes, offset)	Read indicated number of bytes at offset from the file
`read_buffer`(self[, nbytes])	Read from buffer.
`readable`(self)
`readall`(self)
`readinto`(self, b)	Read into the supplied buffer
`readline`(self[, size])	NOT IMPLEMENTED.
`readlines`(self[, hint])	NOT IMPLEMENTED.
`resize`(self, new_size)	Resize the map and underlying file.
`seek`(self, int64_t position, int whence=0)	Change current file stream position
`seekable`(self)
`size`(self)	Return file size
`tell`(self)	Return current stream position
`truncate`(self)	NOT IMPLEMENTED
`upload`(self, stream[, buffer_size])	Write from a source stream to this file.
`writable`(self)
`write`(self, data)	Write data to the file.
`writelines`(self, lines)	Write lines to the file.

Attributes

`closed`
`mode`	The file mode.

close(self)#

closed#

static create(path, size)#

Create a MemoryMappedFile

Parameters:

pathstr: Where to create the file.
sizeint: Size of the memory mapped file.

download(self, stream_or_path, buffer_size=None)#

Read this file completely to a local path or destination stream.

This method first seeks to the beginning of the file.

Parameters:

stream_or_pathstr or file-like object: If a string, a local file path to write to; otherwise, should be a writable stream.
buffer_sizeint, optional: The buffer size to use for data transfers.

fileno(self)#

flush(self)#

Flush the stream, if applicable.

An error is raised if stream is not writable.

get_stream(self, file_offset, nbytes)#

Return an input stream that reads a file segment independent of the state of the file.

Allows reading portions of a random access file as an input stream without interfering with each other.

Parameters:

file_offsetint
nbytesint

Returns:

streamNativeFile

isatty(self)#

metadata(self)#: Return file metadata

mode#

The file mode. Currently instances of NativeFile may support:

rb: binary read
wb: binary write
rb+: binary read and write

read(self, nbytes=None)#

Read and return up to n bytes.

If nbytes is None, then the entire remaining file contents are read.

Parameters:

nbytesint, default None

Returns:

databytes

read1(self, nbytes=None)#

Read and return up to n bytes.

Unlike read(), if nbytes is None then a chunk is read, not the entire file.

Parameters:

nbytesint, default None: The maximum number of bytes to read.

Returns:

databytes

read_at(self, nbytes, offset)#

Read indicated number of bytes at offset from the file

Parameters:

nbytesint
offsetint

Returns:

databytes

read_buffer(self, nbytes=None)#

Read from buffer.

Parameters:

nbytesint, optional: maximum number of bytes read

readable(self)#

readall(self)#

readinto(self, b)#

Read into the supplied buffer

Parameters:

bbuffer-like object: A writable buffer object (such as a bytearray).

Returns:

writtenint: number of bytes written

readline(self, size=None)#

NOT IMPLEMENTED. Read and return a line of bytes from the file.

If size is specified, read at most size bytes.

Line terminator is always b”n”.

Parameters:

sizeint: maximum number of bytes read

readlines(self, hint=None)#

NOT IMPLEMENTED. Read lines of the file

Parameters:

hintint: maximum number of bytes read until we stop

resize(self, new_size)#

Resize the map and underlying file.

Parameters:

new_sizenew size in bytes

seek(self, int64_t position, int whence=0)#

Change current file stream position

Parameters:

positionint: Byte offset, interpreted relative to value of whence argument
whenceint, default 0: Point of reference for seek offset

Returns:

int: The new absolute stream position.

Notes

Values of whence: * 0 – start of stream (the default); offset should be zero or positive * 1 – current stream position; offset may be negative * 2 – end of stream; offset is usually negative

seekable(self)#

size(self)#: Return file size

tell(self)#: Return current stream position

truncate(self)#: NOT IMPLEMENTED

upload(self, stream, buffer_size=None)#

Write from a source stream to this file.

Parameters:

streamfile-like object: Source stream to pipe to this file.
buffer_sizeint, optional: The buffer size to use for data transfers.

writable(self)#

write(self, data)#

Write data to the file.

Parameters:

databytes-like object or exporter of buffer protocol

Returns:

int: nbytes: number of bytes written

writelines(self, lines)#

Write lines to the file.

Parameters:

linesiterable: Iterable of bytes-like objects or exporters of buffer protocol