Why Does My Parameterized SQL Query Throw a 'TypeError: Not All Arguments Converted' Error?

TypeError: Not All Arguments Converted During String Formatting in Parameterized SQL Queries

Encountering the error "TypeError: not all arguments converted during string formatting" when using strings in a parameterized SQL query is a common issue.

The code example provided:

cur.execute("SELECT * FROM records WHERE email LIKE '%s'", search)

attempts to execute a query with a string formatted with a placeholder (%s) for the search parameter. However, this method is incorrect.

To resolve this error, the correct way to execute a parameterized query is to provide the placeholder values as a list:

cur.execute("SELECT * FROM records WHERE email LIKE %s", [search])

In this case, [search] is a list containing the single search parameter. MySQLdb (and other similar database libraries) expect a list of values to be converted and formatted. Passing a single value directly will result in the error.

The reasoning behind this is that a parameterized query can contain multiple placeholders in the SQL statement, each representing a different value. By providing the values as a list, the database library can iterate over the list and convert each value appropriately.

Therefore, when using placeholders in parameterized SQL queries, it is essential to provide the values as a list or tuple. This ensures that all arguments are correctly converted and formatted, preventing the "not all arguments converted" error.

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