Troubleshooting Parameter Substitution Issues in SQLite

Encountering issues when utilizing parameter substitution in SQLite3 with Python? Here's an in-depth investigation and a resolution.

In an attempt to prevent SQL injections, parameter substitution using '?' is advisable. However, an error may arise when utilizing this approach. For instance, with the following code:

for item in self.inventory_names:
    self.cursor.execute("SELECT weight FROM Equipment WHERE name = ?", item)
    self.cursor.close()

The error "sqlite3.ProgrammingError: Incorrect number of bindings supplied" occurs, indicating that the statement specifies one binding, whereas eight are provided. This issue stems from the initial creation of the database table. The module responsible for database creation contains eight bindings, which leads to the mismatch.

cursor.execute("""CREATE TABLE Equipment 
    (id INTEGER PRIMARY KEY, 
    name TEXT,
    price INTEGER, 
    weight REAL, 
    info TEXT, 
    ammo_cap INTEGER, 
    availability_west TEXT,
    availability_east TEXT)""")

Ironically, substituting '?' with a less secure '%s' resolves the problem:

for item in self.inventory_names:
    self.cursor.execute("SELECT weight FROM Equipment WHERE name = '%s'" % item)
    self.cursor.close()

The reason behind this paradox lies in the way Cursor.execute() accepts its second parameter. Instead of a single string, it expects a sequence, but you are passing a string of length eight.

To rectify this issue, adjust the code to the following:

self.cursor.execute("SELECT weight FROM Equipment WHERE name = ?", [item])

This modification ensures that the parameter substitution works as intended. Always ensure that the second parameter passed to Cursor.execute() corresponds to the specified number of bindings in the SQL statement.