Variable assignment within a while loop

Question

What would be the closest pattern to doing the above in python?

while (item=self.cursor.fetchone()):
    print item['id']

Basically, I'd like to get the result of a single database-row. What would be the most direct way to do this, or do I need to have some generic loop like while 1?

Python will add an assignment expression in Python 3.8. Before that, assignments were *always statements*. If you don't have that, then `item = cursor.fetchone(); while item: ....; item = cursor.fetchone()` — juanpa.arrivillaga, Sep 10 '19 at 19:43
As an aside, this was a highly controversial addition to the language. Apparently, the furor over PEP 572's adoption was so great that it was a main motivation behind Guido van Rossum stepping down as BDFL. https://lwn.net/Articles/759654/ — juanpa.arrivillaga, Sep 10 '19 at 19:46
@RomanPerekhrest good question, as some DB adaptor api's support direct iteration over the cursor to obtain results row-by-row. — juanpa.arrivillaga, Sep 10 '19 at 19:46
It would be wise to add a respective DB engine name to a list of tags in your case — RomanPerekhrest, Sep 10 '19 at 19:48

score 1 · Accepted Answer · answered Sep 10 '19 at 19:52

There's a comprehensive section on MySQLCursor.fetchone() doc page:

The following example shows two equivalent ways to process a query result. The first uses fetchone() in a while loop, the second uses the cursor as an iterator:

# Using a while loop
cursor.execute("SELECT * FROM employees")
row = cursor.fetchone()
while row is not None:
    print(row)
    row = cursor.fetchone()

# Using the cursor as iterator
cursor.execute("SELECT * FROM employees")
for row in cursor:
    print(row)

Got it -- thanks for this very clear example and the two options. The second option is pretty neat, I had never seen that style done before. — David542, Sep 10 '19 at 20:01

Variable assignment within a while loop

1 Answers1