Python in a Nutshell

Name

open

Synopsis

open(filename,flag='r',mode=0666)

Opens or creates the DBM file named by filename (a string that can denote any path to a file, not just a name), and returns a suitable mapping object corresponding to the DBM file. When the DBM file already exists, open uses module whichdb to determine which DBM library can handle the file. When open creates a new DBM file, open chooses the first available DBM module in order of preference: dbhash, gdbm, dbm, and dumbdbm.

flag is a one-character string that tells open how to open the file and whether to create it, as shown in Table 11-1. mode is an integer that open uses as the file’s permission bits if open creates the file, as covered in Section 10.2.2 in Chapter 10. Not all DBM modules use flags and mode, but for portability’s sake you should always supply appropriate values for these arguments when you call anydbm.open.

Table 11-1. flag values for anydbm.open

Flag	Read-only?	If file exists	If file does not exist
'r'	yes	open opens the file	open raises error
'w'	no	open opens the file	open raises error
'c'	no	open opens the file	open creates the file
'n'	no	open truncates the file	open creates the file

anydbm.open returns a mapping object m that supplies a subset of the functionality of dictionaries (covered in Chapter 4). m only accepts strings as keys and values, and the only mapping methods m supplies are m .has_key and m .keys. However, you can bind, rebind, access, and unbind items in m with the ...