Question

I have a Python function which receives numerous variables, and builds an SQL query out of them:

def myfunc(name=None, abbr=None, grade=None, ...)

These values should build an SQL query. For that purpose, Those who equal None should be changed to NULL, and those who store useful values should be embraced with 's:

name="'"+name+"\'" if name else 'NULL'
abbr="'"+abbr+"\'" if abbr else 'NULL'
...
Lots of lines here - that's my problem!
...

And than,

query="""INSERT INTO table(name, abbr, ...)
         VALUES (%(name)s, %(abbr)s, ...) """ locals()
cur.execute(query)

Is there a nicer, more Pythonic way to change the variable contents according to this rule?

Adam

Answer 1

The best way to form a SQL query is not by string-formatting — the execute method of a cursor object takes a query string with placeholders and a sequence (or dict, depending on the exact implementation you have of the DB API) with the values to substitute there; it will then perform the None-to-Null and string-quoting that you require.

I strongly recommend you look into that possibility. If you need string processing for some other purpose, however, you could do something like:

processed = dict((n, "'%s'" % v if v is not None else 'NULL')
                 for n, v in locals().iteritems())

and then use dictionary processed instead of locals() for further string-formatting.