error: db type could not be determined

[neutrinman]

why does the following error occur?

def quit_time():
data_file = shelve.open("da ta.dat", "c")
data_file["quit_time"] = datetime.dateti me.today()
print data_file["quit_time"]
raw_input("ente r")
Traceback (most recent call last):
File "D:\a\TEXT\Py\g oing_over\going _over.py", line 192, in -toplevel-
main()
File "D:\a\TEXT\Py\g oing_over\going _over.py", line 190, in main
quit_time()
File "D:\a\TEXT\Py\g oing_over\going _over.py", line 156, in quit_time
data_file = shelve.open("da ta.dat", "c")
File "D:\A\UTILITIES \PYTHON\PYTHON2 3J\lib\shelve.p y", line 231, in
open
return DbfilenameShelf (filename, flag, protocol, writeback, binary)
File "D:\A\UTILITIES \PYTHON\PYTHON2 3J\lib\shelve.p y", line 212, in
__init__
Shelf.__init__( self, anydbm.open(fil ename, flag), protocol,
writeback, binary)
File "D:\A\UTILITIES \PYTHON\PYTHON2 3J\lib\anydbm.p y", line 80, in
open
raise error, "db type could not be determined"
error: db type could not be determined

[John Machin]

ne********@myre albox.com wrote:

why does the following error occur?

I don't know; I've never used the shelve module. Let's see what as two
utter n00bz we can find out. Let's check out where it clagged:
lib\anydbm.py, line 80, in open ...

Hmm, reading backwards a little, looks like it called whichdb.whichdb
to nut out what sort of database it was, and whichdb reported back that
it was an existing file, of unknown type. Flicking through whichdb.py
confirms this.

Let's see if we can reproduce that:

=== step 1: file doesn't exist ===
C:\junk>c:\pyth on23\python
Python 2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit (Intel)]
on win32
Type "help", "copyright" , "credits" or "license" for more information.

import shelve
df = shelve.open('my data.dat', 'c')
^Z
C:\junk>dir mydata.dat
[snip]
26/02/2005 08:40p 24,576 mydata.dat

=== looks like file created OK ==

C:\junk>del mydata.dat
C:\junk>copy con mydata.dat
any old codswallop
^Z
1 file(s) copied.

=== OK, now mydata.dat is trash.

C:\junk>c:\pyth on23\python
Python 2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit (Intel)]
on win32
Type "help", "copyright" , "credits" or "license" for more information. import shelve
df = shelve.open('my data.dat', 'c') Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "c:\python23\li b\shelve.py", line 231, in open
return DbfilenameShelf (filename, flag, protocol, writeback, binary)
File "c:\python23\li b\shelve.py", line 212, in __init__
Shelf.__init__( self, anydbm.open(fil ename, flag), protocol,
writeback, binary)
File "c:\python23\li b\anydbm.py", line 80, in open
raise error, "db type could not be determined"
anydbm.error: db type could not be determined

Uh-huh.

By the way, it's probably not a good idea to use a ".dat" extension;
evidently (read whichdb.py for the gory details) some of the dbms add
an extension to the supplied name. One of them uses ".dat". Could
become a source of confusion.

Take a hint: they say "Google is your friend", but better still is the
source in lib\*.py -- it's quite legible, you don't need an Internet
connection, and there sure ain't no ads in the margin. And don't just
open it in emergencies: pick a module that covers a topic that
interests you and just read it. You'll see good coding style, good ways
of doing things, wise utterances by the timbot, ...

HTH,
John