Return variable from cx_Oracle PL/SQL call in Python

Question

I want to execute an Oracle PL/SQL statement via cx_oracle in Python. Code looks like this:

db = cx_Oracle.connect(user, pass, dsn_tns)
cursor = db.cursor()
         


        

Answer 1

You need a function to return a result. An anonymous block will not.

You need to create a function in the database, for instance:

create or replace function calculation return number is
  c   number := 0.2;
  mn  number := 1.5;
  res number;
begin
  return c + mn / 6.;
end;
/

Then change your Python code to call the function, using, callfunc()

db = cx_Oracle.connect(user, pass, dsn_tns)
cursor = db.cursor()

try:
  result = cursor.callfunc('calculation', float)
  print result
except cx_Oracle.DatabaseError as e:
  err, = e.args
  print "\n".join([str(err.code),err.message,err.context])

---

It's not possible to create a function on the fly but your function is simple enough that you can do it in a select statement and use fetchall() as described in the linked documentation to return the result to Python. fetchall() returns a list of tuples so if you're only after a single row and column you can immediately select the 0^th index of both.

>>> import cx_Oracle
>>> db = cx_Oracle.connect('****','****','****')
>>> cursor = db.cursor()
>>> SQL = """select 0.2 + 1.5 / 6. from dual"""
>>> try:
...     cursor.execute(SQL)
...     result = cursor.fetchall()[0][0]
... except cx_Oracle.DataBaseError, e:
...     pass
...
<__builtin__.OracleCursor on >
>>> result
0.45000000000000001
>>>

You can also pass the variables into your execute() call using bind variables and therefore instantiate them in Python if necessary:

>>> c = 0.2
>>> mn = 1.5
>>> SQL = """select :c + :mn / 6. from dual"""
>>> bind_vars = { 'c' : c, 'mn' : mn }
>>> cursor.execute(SQL, bind_vars)
<__builtin__.OracleCursor on >
>>> result = cursor.fetchall()[0][0]
>>> result
0.45000000000000001
>>>

Though it might be simpler to do all this in Python... I assume your actual situation is more complicated?