More pythonic way to iterate

Question

I am using a module that is part of a commercial software API. The good news is there is a python module - the bad news is that its pretty unpythonic.

To iterate over rows, the follwoing syntax is used:

cursor = gp.getcursor(table)
row =  cursor.next()
while row:
    #do something with row
    row = cursor.next()

What is the most pythonic way to deal with this situation? I have considered creating a first class function/generator and wrapping calls to a for loop in it:

def cursor_iterator(cursor):
    row =  cursor.next()
    while row:
        yield row
        row = cursor.next()

[...]

cursor = gp.getcursor(table)
for row in cursor_iterator(cursor):
    # do something with row

This is an improvement, but feels a little clumsy. Is there a more pythonic approach? Should I create a wrapper class around the table type?

Mmmh cursor.next() looks like you might be able to do for row in cursor: — Felix Kling
– Felix Kling, Commented Jun 5, 2010 at 10:56
@Felix, nope. next doesn't raise a StopIteration, so after the real data, that would just loop forever with row being None. — Matthew Flaschen
– Matthew Flaschen, Commented Jun 5, 2010 at 11:00
@Felix King: Almost, but because an iterator signals termination by raising StopIteration, for row in cursor: will iterate over the rows, then give an infinite stream of Nones. — user97370
– user97370, Commented Jun 5, 2010 at 11:00

user97370 · Accepted Answer · 2010-06-05 10:54:31Z

11

Assuming that one of Next and next is a typo and they're both the same, you can use the not-so-well-known variant of the built-in iter function:

for row in iter(cursor.next, None):
    <do something>

answered Jun 5, 2010 at 10:54

user97370

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1 Comment

fmark Over a year ago

Great answer! Yep, the functions are the same (worse still, they are somehow case insensitive!).

Felix Kling · Accepted Answer · 2010-06-05 11:50:56Z

2

You could create a custom wrapper like:

class Table(object):
    def __init__(self, gp, table):
        self.gp = gp
        self.table = table
        self.cursor = None

   def __iter__(self):
        self.cursor = self.gp.getcursor(self.table)
        return self

   def next(self):
        n = self.cursor.next()
        if not n:
             raise StopIteration()
        return n

and then:

for row in Table(gp, table)

See also: Iterator Types

edited Jun 5, 2010 at 11:50

answered Jun 5, 2010 at 11:01

Felix Kling

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1 Comment

fmark Over a year ago

I like this approach also. I might consider wrapping gp in this manner if I need to wrap more than just the cursor iteration.

Olivier Verdier · Accepted Answer · 2010-06-05 10:57:20Z

1

The best way is to use a Python iterator interface around the table object, imho:

class Table(object):
    def __init__(self, table):
         self.table = table

    def rows(self):
        cursor = gp.get_cursor(self.table)
        row =  cursor.Next()
        while row:
            yield row
            row = cursor.next()

Now you just call:

my_table = Table(t)
for row in my_table.rows():
     # do stuff with row

It's very readable, in my opinion.

answered Jun 5, 2010 at 10:57

Olivier Verdier

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