diff -r ffa851df0825 -r 2fb8b9db1c86 symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/mmap.rst --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/mmap.rst Fri Jul 31 15:01:17 2009 +0100 @@ -0,0 +1,247 @@ + +:mod:`mmap` --- Memory-mapped file support +========================================== + +.. module:: mmap + :synopsis: Interface to memory-mapped files for Unix and Windows. + + +Memory-mapped file objects behave like both strings and like file objects. +Unlike normal string objects, however, these are mutable. You can use mmap +objects in most places where strings are expected; for example, you can use +the :mod:`re` module to search through a memory-mapped file. Since they're +mutable, you can change a single character by doing ``obj[index] = 'a'``, or +change a substring by assigning to a slice: ``obj[i1:i2] = '...'``. You can +also read and write data starting at the current file position, and +:meth:`seek` through the file to different positions. + +A memory-mapped file is created by the :class:`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 :meth:`fileno` method to obtain the correct value for the +*fileno* parameter. Otherwise, you can open the file using the +:func:`os.open` function, which returns a file descriptor directly (the file +still needs to be closed when done). + +For both the Unix and Windows versions of the constructor, *access* may be +specified as an optional keyword parameter. *access* accepts one of three +values: :const:`ACCESS_READ`, :const:`ACCESS_WRITE`, or :const:`ACCESS_COPY` +to specify read-only, write-through or copy-on-write memory respectively. +*access* can be used on both Unix and Windows. If *access* is not specified, +Windows mmap returns a write-through mapping. The initial memory values for +all three access types are taken from the specified file. Assignment to an +:const:`ACCESS_READ` memory map raises a :exc:`TypeError` exception. +Assignment to an :const:`ACCESS_WRITE` memory map affects both memory and the +underlying file. Assignment to an :const:`ACCESS_COPY` memory map affects +memory but does not update the underlying file. + +.. versionchanged:: 2.5 + To map anonymous memory, -1 should be passed as the fileno along with the + length. + +.. versionchanged:: 2.6 + mmap.mmap has formerly been a factory function creating mmap objects. Now + mmap.mmap is the class itself. + +.. class:: mmap(fileno, length[, tagname[, access[, offset]]]) + + **(Windows version)** Maps *length* bytes from the file specified by the + file handle *fileno*, and creates a mmap object. If *length* is larger + than the current size of the file, the file is extended to contain *length* + bytes. If *length* is ``0``, the maximum length of the map is the current + size of the file, except that if the file is empty Windows raises an + exception (you cannot create an empty mapping on 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 or ``None``, the mapping is created without a name. Avoiding the + use of the tag 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. + + +.. class:: mmap(fileno, length[, flags[, prot[, access[, offset]]]]) + :noindex: + + **(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 when + :class:`mmap` is called. + + *flags* specifies the nature of the mapping. :const:`MAP_PRIVATE` creates a + private copy-on-write mapping, so changes to the contents of the mmap + object will be private to this process, and :const:`MAP_SHARED` creates a + mapping that's shared with all other processes mapping the same areas of + the file. The default value is :const:`MAP_SHARED`. + + *prot*, if specified, gives the desired memory protection; the two most + useful values are :const:`PROT_READ` and :const:`PROT_WRITE`, to specify + that the pages may be read or written. *prot* defaults to + :const:`PROT_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 the PAGESIZE or + ALLOCATIONGRANULARITY. + + This example shows a simple way of using :class:`mmap`:: + + import mmap + + # write a simple example file + with open("hello.txt", "w") as f: + f.write("Hello Python!\n") + + with open("hello.txt", "r+") as f: + # memory-map the file, size 0 means whole file + map = mmap.mmap(f.fileno(), 0) + # read content via standard file methods + print map.readline() # prints "Hello Python!" + # read content via slice notation + print map[:5] # prints "Hello" + # update content using slice notation; + # note that new content must have same size + map[6:] = " world!\n" + # ... and read again using standard file methods + map.seek(0) + print map.readline() # prints "Hello world!" + # close the map + map.close() + + + The next example demonstrates how to create an anonymous map and exchange + data between the parent and child processes:: + + import mmap + import os + + map = mmap.mmap(-1, 13) + map.write("Hello world!") + + pid = os.fork() + + if pid == 0: # In a child process + map.seek(0) + print map.readline() + + map.close() + + + Memory-mapped file objects support the following methods: + + + .. method:: close() + + Close the file. Subsequent calls to other methods of the object will + result in an exception being raised. + + + .. method:: find(string[, start[, end]]) + + Returns the lowest index in the object where the substring *string* is + found, such that *string* is contained in the range [*start*, *end*]. + Optional arguments *start* and *end* are interpreted as in slice notation. + Returns ``-1`` on failure. + + + .. method:: 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. + + **(Windows version)** A nonzero value returned indicates success; zero + indicates failure. + + **(Unix version)** A zero value is returned to indicate success. An + exception is raised when the call failed. + + + .. method:: move(dest, src, count) + + Copy the *count* bytes starting at offset *src* to the destination index + *dest*. If the mmap was created with :const:`ACCESS_READ`, then calls to + move will throw a :exc:`TypeError` exception. + + + .. method:: read(num) + + Return a string containing up to *num* bytes starting from the current + file position; the file position is updated to point after the bytes that + were returned. + + + .. method:: read_byte() + + Returns a string of length 1 containing the character at the current file + position, and advances the file position by 1. + + + .. method:: readline() + + Returns a single line, starting at the current file position and up to the + next newline. + + + .. method:: resize(newsize) + + Resizes the map and the underlying file, if any. If the mmap was created + with :const:`ACCESS_READ` or :const:`ACCESS_COPY`, resizing the map will + throw a :exc:`TypeError` exception. + + + .. method:: rfind(string[, start[, end]]) + + Returns the highest index in the object where the substring *string* is + found, such that *string* is contained in the range [*start*, *end*]. + Optional arguments *start* and *end* are interpreted as in slice notation. + Returns ``-1`` on failure. + + + .. method:: seek(pos[, whence]) + + Set the file's current position. *whence* argument is optional and + defaults to ``os.SEEK_SET`` or ``0`` (absolute file positioning); other + values are ``os.SEEK_CUR`` or ``1`` (seek relative to the current + position) and ``os.SEEK_END`` or ``2`` (seek relative to the file's end). + + + .. method:: size() + + Return the length of the file, which can be larger than the size of the + memory-mapped area. + + + .. method:: tell() + + Returns the current position of the file pointer. + + + .. method:: write(string) + + Write the bytes in *string* into memory at the current position of the + file pointer; the file position is updated to point after the bytes that + were written. If the mmap was created with :const:`ACCESS_READ`, then + writing to it will throw a :exc:`TypeError` exception. + + + .. method:: write_byte(byte) + + Write the single-character string *byte* into memory at the current + position of the file pointer; the file position is advanced by ``1``. If + the mmap was created with :const:`ACCESS_READ`, then writing to it will + throw a :exc:`TypeError` exception. + +