> Is it really backward compatible? Have you tried?
I tried basic integer indexing and slicing, which work as expected, as
does the dictionary interface. I just went through all the scenarios I
could think of and found two differences with DictCursor.
1) Extended slicing fails with an exception (e.g., row[2:5:2] or
row[::-1]).
2) DictCursor objects have the unfortunate list behavior that they
can't be used directly for string interpolation, whereas tuples can.
--David
Here are the details. Starting with a simple query,
>>> import psycopg2
>>> query = ('select id, first_name, last_name, email, password, '
... 'registration_key from auth_user;')
check the default behavior.
>>> conn = psycopg2.connect('')
>>> cursor = conn.cursor()
>>> cursor.execute(query)
>>> rs = cursor.fetchall()
>>> row = rs[0]
>>> row
(1, 'Joe', 'Demo', '[email protected]',
'4352cd32e514b98bf6d88ccde0775bf3', '')
Rows are plain tuples by default.
>>> type(row)
<type 'tuple'>
>>> default_row = row # preserve the row for later
Now try with DictConnection.
>>> import psycopg2.extras
>>> conn = psycopg2.extras.DictConnection('')
>>> cursor = conn.cursor()
>>> cursor.execute(query)
>>> rs = cursor.fetchall()
>>> row = rs[0]
>>> type(row)
<class 'psycopg2.extras.DictRow'>
Results are now DictRows instead of tuples. DictRows repr like lists.
>>> row
[1, 'Joe', 'Demo', '[email protected]',
'4352cd32e514b98bf6d88ccde0775bf3', '']
And they have list methods. (Tuples have no non-special methods so
this seems ok.
>>> row.index('Joe')
1
They convert nicely to other builtins.
>>> list(row)
[1, 'Joe', 'Demo', '[email protected]',
'4352cd32e514b98bf6d88ccde0775bf3', '']
>>> tuple(row)
(1, 'Joe', 'Demo', '[email protected]',
'4352cd32e514b98bf6d88ccde0775bf3', '')
>>> dict(row)
{'first_name': 'Joe', 'last_name': 'Demo', 'id': 1, 'password':
'4352cd32e514b98bf6d88ccde0775bf3', 'registration_key': '', 'email':
'[email protected]'}
Integer indexing and len() works.
>>> row[0], row[1], row[2], row[3], row[4], row[5]
(1, 'Joe', 'Demo', '[email protected]',
'4352cd32e514b98bf6d88ccde0775bf3', '')
>>> len(row)
6
They also have a dict interface.
>>> row.keys()
['first_name', 'last_name', 'email', 'password',
'registration_key', 'id']
>>> row['first_name'], row['last_name'], row['id']
('Joe', 'Demo', 1)
Slicing works as expected.
>>> row[:3]
[1, 'Joe', 'Demo']
>>> row[-3:]
['[email protected]', '4352cd32e514b98bf6d88ccde0775bf3', '']
>>> row[2:5]
['Demo', '[email protected]', '4352cd32e514b98bf6d88ccde0775bf3']
Hmmm, extended slicing fails (Strike 1)...
>>> row[2:5:-1]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.5/site-packages/psycopg2/extras.py", line
110, in __getitem__
x = self._index[x]
TypeError: unhashable type
>>> row[2:5:1]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.5/site-packages/psycopg2/extras.py", line
110, in __getitem__
x = self._index[x]
TypeError: unhashable type
but it works for regular tuples.
>>> default_row[2:5:1]
('Demo', '[email protected]', '4352cd32e514b98bf6d88ccde0775bf3')
>>> default_row[2:5:-1]
()
Another problem is the difference between tuples and lists when doing
string interpolation. String interpolation requires a tuple and fails
with a list. For example,
>>> '%s %s' % ('a', 'b')
'a b'
>>> '%s %s' % ['a', 'b']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: not enough arguments for format string
The DictCursor fails with string interpolation, just like a list
(Strike 2),
>>> '%s %s %s %s %s %s' % row
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: not enough arguments for format string
but works when wrapped with tuple().
>>> '%s %s %s %s %s %s' % tuple(row)
'1 Joe Demo [email protected] 4352cd32e514b98bf6d88ccde0775bf3 '
It was pretty easy to find two ways DictCursor wouldn't be completely
backward compatible. It's probably safe to bet there are other edge
cases that could be found.
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"web2py Web Framework" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/web2py?hl=en
-~----------~----~----~----~------~----~------~--~---
