random-access

Is there a Python file type for accessing random lines without traversing the whole file? I need to search within a large file, reading the whole thing into memory wouldn't be possible. Any types or methods would be appreciated. This seems like just the sort of thing mmap was designed for. A mmap object creates a string-like interface to a file: >>> f = open("bonnie.txt", "wb") >>> f.write("My Bonnie lies over the ocean.") >>> f.close() >>> f.open("bonnie.txt", "r+b") >>> mm = mmap(f.fileno(), 0) >>> print mm[3:9] Bonnie In case you were wondering, mmap objects can also be assigned to: >>>

RandomAccessFile is quite slow for random access to a file. You often read about implementing a buffered layer over it, but code doing this isn't possible to find online. So my question is: would you guys who know any opensource implementation of this class share a pointer or share your own implementation? It would be nice if this question would turn out as a collection of useful links and code about this problem, which I'm sure, is shared by many and never addressed properly by SUN. Please, no reference to MemoryMapping, as files can be way bigger than Integer.MAX_VALUE. Edwin Dalorzo Well, I

In MySQL I can use the RAND() function, is there any alternative in SQLite 3? dfa using random() : SELECT foo FROM bar WHERE id >= (abs(random()) % (SELECT max(id) FROM bar)) LIMIT 1; EDIT (by QOP): Since the docs on SQLite Autoincrement ed columns states that: The normal ROWID selection algorithm described above will generate monotonically increasing unique ROWIDs as long as you never use the maximum ROWID value and you never delete the entry in the table with the largest ROWID. If you ever delete rows, then ROWIDs from previously deleted rows might be reused when creating new rows . The

I have a table in postgres that contains couple of millions of rows. I have checked on the internet and I found the following SELECT myid FROM mytable ORDER BY RANDOM() LIMIT 1; it works, but it's really slow... is there another way to make that query, or a direct way to select a random row without reading all the table? by the way 'myid' is an integer but it can be an empty field. thanks NPE You might want to experiment with OFFSET , as in SELECT myid FROM mytable OFFSET floor(random()*N) LIMIT 1; The N is the number of rows in mytable . You may need to first do a SELECT COUNT(*) to figure