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
– juanpa.arrivillaga, Commented Sep 10, 2019 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. lwn.net/Articles/759654 — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Sep 10, 2019 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
– juanpa.arrivillaga, Commented Sep 10, 2019 at 19:46
It would be wise to add a respective DB engine name to a list of tags in your case — RomanPerekhrest
– RomanPerekhrest, Commented Sep 10, 2019 at 19:48

RomanPerekhrest · Accepted Answer · 2019-09-10 19:52:29Z

1

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)

answered Sep 10, 2019 at 19:52

RomanPerekhrest

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1 Comment

David542 Over a year ago

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.

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