Python sqlite3.Cursor.setinputsizes Method
Last modified April 15, 2025
This guide explores Python's sqlite3.Cursor.setinputsizes
method,
which is part of the DB-API 2.0 specification but not implemented in SQLite.
Basic Definitions
The setinputsizes
method is defined in Python's DB-API 2.0 as a way
to predefine memory areas for parameter binding. It's meant to optimize repeated
executions of the same statement.
In SQLite's implementation, this method does nothing as SQLite handles parameter binding dynamically. The method exists for API compatibility but has no effect.
Method Signature
The method signature is simple: setinputsizes(sizes)
where sizes can
be a sequence or None. The sizes parameter specifies the expected data types.
Despite being callable, the method performs no operation in SQLite. It's present to maintain compatibility with the DB-API 2.0 specification.
Basic Usage
This example demonstrates calling the method with different parameter types. Despite the calls, they have no effect on SQLite operations.
import sqlite3 with sqlite3.connect(':memory:') as conn: with conn.cursor() as cur: # These calls do nothing in SQLite cur.setinputsizes(None) cur.setinputsizes([sqlite3.TEXT, sqlite3.INTEGER]) cur.setinputsizes(50) # Arbitrary size # Execute a query normally cur.execute("CREATE TABLE test (id INTEGER, name TEXT)") cur.execute("INSERT INTO test VALUES (?, ?)", (1, 'Alice'))
The example shows that setinputsizes
can be called but doesn't
affect subsequent operations. SQLite handles parameter binding dynamically.
With execute
This example attempts to use setinputsizes
before executing a query.
The method call has no impact on the execution.
import sqlite3 with sqlite3.connect(':memory:') as conn: with conn.cursor() as cur: cur.execute("CREATE TABLE data (id INTEGER, value REAL)") # Set input sizes (no effect) cur.setinputsizes([sqlite3.INTEGER, sqlite3.REAL]) # Insert data works the same with or without setinputsizes cur.execute("INSERT INTO data VALUES (?, ?)", (1, 3.14159)) # Verify insertion cur.execute("SELECT * FROM data") print(cur.fetchone()) # (1, 3.14159)
The data insertion works identically whether setinputsizes
is called
or not. SQLite determines parameter types at execution time.
Multiple Parameter Types
This example shows that SQLite ignores the type hints provided to
setinputsizes
and handles type conversion automatically.
import sqlite3 with sqlite3.connect(':memory:') as conn: with conn.cursor() as cur: cur.execute("CREATE TABLE items (id INTEGER, name TEXT, price REAL)") # Set input sizes for different types (ignored) cur.setinputsizes([sqlite3.INTEGER, sqlite3.TEXT, sqlite3.REAL]) # Insert with automatic type conversion cur.execute("INSERT INTO items VALUES (?, ?, ?)", ('1', 42.99, '3.50')) # Note reversed types # The values are stored correctly despite type hints cur.execute("SELECT * FROM items") print(cur.fetchone()) # (1, '42.99', 3.5)
SQLite performs type conversion regardless of the setinputsizes
calls. The method doesn't enforce or influence type handling in SQLite.
With executemany
This example demonstrates that setinputsizes
has no effect on batch
operations using executemany
.
import sqlite3 data = [ (1, 'Apple', 0.99), (2, 'Banana', 0.59), (3, 'Cherry', 1.99) ] with sqlite3.connect(':memory:') as conn: with conn.cursor() as cur: cur.execute("CREATE TABLE products (id INTEGER, name TEXT, price REAL)") # Set input sizes (no effect) cur.setinputsizes([sqlite3.INTEGER, sqlite3.TEXT, sqlite3.REAL]) # Batch insert works normally cur.executemany("INSERT INTO products VALUES (?, ?, ?)", data) # Verify all rows inserted cur.execute("SELECT COUNT(*) FROM products") print(cur.fetchone()[0]) # 3
The executemany
operation proceeds normally regardless of the
setinputsizes
call. SQLite handles each parameter set dynamically.
With Custom Types
This example shows that setinputsizes
doesn't affect custom type
adapters in SQLite.
import sqlite3 import datetime # Register custom adapter sqlite3.register_adapter(datetime.date, lambda d: d.isoformat()) with sqlite3.connect(':memory:') as conn: with conn.cursor() as cur: cur.execute("CREATE TABLE events (id INTEGER, date TEXT)") # Set input sizes (ignored) cur.setinputsizes([sqlite3.INTEGER, sqlite3.TEXT]) # Custom type conversion still works today = datetime.date.today() cur.execute("INSERT INTO events VALUES (?, ?)", (1, today)) # Verify date stored correctly cur.execute("SELECT date FROM events WHERE id = 1") print(cur.fetchone()[0]) # ISO formatted date
The custom date adapter works regardless of the setinputsizes
call.
SQLite's type adaptation system operates independently of this method.
Performance Comparison
This example demonstrates that setinputsizes
doesn't provide any
performance benefit in SQLite, unlike some other database systems.
import sqlite3 import time def time_inserts(use_setinputsizes): with sqlite3.connect(':memory:') as conn: with conn.cursor() as cur: cur.execute("CREATE TABLE nums (n INTEGER)") if use_setinputsizes: cur.setinputsizes([sqlite3.INTEGER]) start = time.time() for i in range(1000): cur.execute("INSERT INTO nums VALUES (?)", (i,)) conn.commit() return time.time() - start # Compare execution times time_with = time_inserts(True) time_without = time_inserts(False) print(f"With setinputsizes: {time_with:.4f}s") print(f"Without setinputsizes: {time_without:.4f}s")
The execution times will be nearly identical, showing that
setinputsizes
provides no performance optimization in SQLite.
Error Handling
This example shows that setinputsizes
doesn't validate parameters
or affect error handling in SQLite.
import sqlite3 with sqlite3.connect(':memory:') as conn: with conn.cursor() as cur: cur.execute("CREATE TABLE test (id INTEGER PRIMARY KEY, data TEXT)") # These calls don't affect error handling cur.setinputsizes([sqlite3.INTEGER, sqlite3.TEXT]) cur.setinputsizes("invalid") # Non-standard parameter try: # This will still raise an error cur.execute("INSERT INTO test VALUES (?, ?)", ("text", 123)) except sqlite3.InterfaceError as e: print(f"Error occurred: {e}")
The example demonstrates that setinputsizes
doesn't prevent or
influence type-related errors in SQLite. Errors are raised during execution.
Best Practices
- Don't rely on it: The method has no effect in SQLite
- Focus on execute(): SQLite handles parameters dynamically
- Use type adapters: For custom type handling instead
- Maintain compatibility: Include it if writing DB-API code
- Document its absence: Note it's non-functional in SQLite
Source References
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