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Errors in Python
Shashank Shanu
a year ago
Table of Content
- Why Python sqlalchemy.exc.ResourceClosedError occurs ?
- Output
- How to solve this error?
Many times,
while performing your tasks in python you surely would come across many
different types of error. In this article, I will try to give you detailed
explanation of one of the error Python sqlalchemy.exc.ResourceClosedError, why
this error occurs and how we can avoid or solve such error while performing our
task.
So, let’s
start…
While
performing any task, there are many possibilities that a user may get an error.
Error is a very good thing as it gives an opportunity to explore many different
aspects and come to a solution. But before solving any error it primes important to know why this error occurred and then only, we can go for it to solve
it.
SQLAlchemy has two main concepts that one must be aware of i.e.,
connections and engines. An engine can support many simultaneous connections. If
we try to bind the table to an engine. Now, whenever we call. Execute function,
a new connection is created for every single query that you execute. But sqlite3
only allows 1 simultaneous "connection". Let me give you a detailed explanation.
Why Python sqlalchemy.exc.ResourceClosedError occurs ?
To understand it better let take an example
engine = create_engine('sqlite:///testdb.db')
metadata = MetaData(bind=engine)
test = Table('test', metadata, autoload=true)
# Select all from pending_data
sel = select([test])
res = engine.execute(sel)
print(res)
# do an insert into pending_data
test.insert().values(info='blah').execute()
Output:
Code Error: Python sqlalchemy.exc.ResourceClosedError There are
many reasons which raise this type of error. Let me explain to you some of them
one by one.
In simple word, one
of the reasons why this error occurs is when we try to read rows from a SQL a statement that does not return any rows.
Example of such
statements are INSERT, UPDATE and DELETE statements that do not return any
column. While a SELECT statement in SQL, on the other hand, should always
return rows, even if the number of rows is zero.
The second reason that raises this error is when the database driver has failed on
a previous statement and the application attempts to continue to use the
database connection without rolling back the transaction first, however, this
requires additional conditions to be in a place that is not easy to replicate
unless the SQL statement is accessing some specific kind of issue.
How to solve this error?
The best way to fix this error is to create the connection and
use it explicitly as shown below. And instead of the automatically created
connections of the engine and to use the connection with the statement, which ensures that the connection
would be closed at the end of the block:
engine = create_engine('sqlite:///testdb.db')
metadata = MetaData(bind=engine)
test = Table('test', metadata, autoload=true)
with engine.connect() as connection:
# Select all from pending_data
sel = select([test])
res = connection.execute(sel)
# do an insert into pending_data
connection.execute(test.insert().values(info='blah'))
I hope after you enjoyed reading this article and finally,
you came to know about Python sqlalchemy.exc.ResourceClosedError.
For more such blogs/courses on data science, machine
learning, artificial intelligence and emerging new technologies do visit us at InsideAIML.
Thanks for reading…
Happy Programming…