Check Decimal.Decimal("NaN"|"sNaN"|"Infinity"|"-Infinity") Parameter.

May 9, 2025 by ADMIN 70 views

Introduction

In this article, we will discuss a bug in PyMySQL that occurs when using decimal.Decimal types with NaN, sNaN, Infinity, or -Infinity values. We will explore the issue, provide a code example to reproduce the bug, and discuss the expected behavior.

Describe the Bug

While PyMySQL handles float("nan"|"inf"|"-inf") correctly and raises an exception before sending the command to the server, it doesn't handle corresponding decimal.Decimal types (NaN, sNaN, Infinity, -Infinity). This can lead to unexpected behavior and errors when working with decimal values in MySQL.

To Reproduce

Here is an example code snippet that demonstrates the bug:

import pymysql
import decimal

con = pymysql.connect(...)  # Replace with your connection settings
cursor = con.cursor()

# Create a float with NaN value
a = float("nan")

# Create a decimal.Decimal with NaN value
b = decimal.Decimal("nan")

try:
    cursor.execute("select %s", (a,))
except Exception as e:
    print(e)
    pass

try:
    cursor.execute("select %s", (b,))
except Exception as e:
    print(e)
    pass

In this code, we create a float with NaN value using float("nan") and a decimal.Decimal with NaN value using decimal.Decimal("nan"). We then attempt to execute a SQL query with these values using the cursor.execute() method.

Expected Behavior

The expected behavior is that both attempts to execute the SQL query with NaN values should raise a NotSupportedError exception with the following message:

Parameter 'nan' for float or decimal types is not supported

This exception should be raised before sending the command to the server, just like when working with float values.

Environment

The bug was observed in PyMySQL version 1.4.5.

Why is this a problem?

The issue with decimal.Decimal types and NaN, sNaN, Infinity, or -Infinity values is that they are not supported by MySQL. When you attempt to use these values in a SQL query, the server will raise an error. By not handling these values correctly, PyMySQL can lead to unexpected behavior and errors when working with decimal values in MySQL.

How to fix the bug?

To fix the bug, you can modify the PyMySQL code to handle decimal.Decimal types with NaN, sNaN, Infinity, or -Infinity values correctly. One possible solution is to raise a NotSupportedError exception with the specified message when encountering these values.

Here is an example of how you can modify the PyMySQL code to fix the bug:

class NotSupportedError(Exception):
    pass

def execute(self, query, args, **kwargs):
    # ...
    if isinstance(args[0], decimal.Decimal) and (args[0] == decimal.Decimal("nan") or args[0] == decimal.Decimal("sNaN") or args[0] == decimal.Decimal("Infinity") or args[0] == decimal.Decimal("-Infinity")):
        raise NotSupportedError("Parameter '{}' for decimal types is not supported".format(args[0]))
    # ...

By making this change, you can ensure that decimal.Decimal types with NaN, sNaN, Infinity, or -Infinity values are handled correctly and raise a NotSupportedError exception with the specified message.

Conclusion

Q: What is the issue with decimal.Decimal types and NaN, sNaN, Infinity, or -Infinity values?

A: The issue is that these values are not supported by MySQL. When you attempt to use them in a SQL query, the server will raise an error. By not handling these values correctly, PyMySQL can lead to unexpected behavior and errors when working with decimal values in MySQL.

Q: Why is PyMySQL not handling decimal.Decimal types with NaN, sNaN, Infinity, or -Infinity values correctly?

A: PyMySQL is not handling these values correctly because it is not checking for them specifically. When you pass a decimal.Decimal object with one of these values to the cursor.execute() method, PyMySQL does not raise an exception or provide any indication that the value is not supported.

Q: What is the expected behavior when using decimal.Decimal types with NaN, sNaN, Infinity, or -Infinity values?

A: The expected behavior is that PyMySQL should raise a NotSupportedError exception with the following message:

Parameter 'nan' for decimal types is not supported

This exception should be raised before sending the command to the server, just like when working with float values.

Q: How can I fix the bug in PyMySQL?

A: To fix the bug, you can modify the PyMySQL code to handle decimal.Decimal types with NaN, sNaN, Infinity, or -Infinity values correctly. One possible solution is to raise a NotSupportedError exception with the specified message when encountering these values.

Q: What is the impact of this bug on my application?

A: The impact of this bug on your application will depend on how you are using decimal values in your SQL queries. If you are passing decimal.Decimal objects with NaN, sNaN, Infinity, or -Infinity values to the cursor.execute() method, your application may raise unexpected errors or behave incorrectly.

Q: How can I prevent this bug from affecting my application?

A: To prevent this bug from affecting your application, you can modify your code to check for NaN, sNaN, Infinity, or -Infinity values before passing them to the cursor.execute() method. You can also consider using a different data type, such as float, that is supported by MySQL.

Q: Is this bug specific to PyMySQL or can it occur with other MySQL drivers?

A: This bug is specific to PyMySQL and may not occur with other MySQL drivers. However, it is possible that other drivers may also have similar issues with decimal.Decimal types and NaN, sNaN, Infinity, or -Infinity values.

Q: How can I report this bug to the PyMySQL developers?

A: To report this bug to the PyMySQL developers, you can submit a bug report on the PyMySQL issue tracker. Be sure to include a clear description of the issue, including any relevant code snippets and error messages.

Q: What is the current status of this bug in PyMySQL?

A: The current status of this in PyMySQL is that it is still present in version 1.4.5. However, the PyMySQL developers may have addressed this issue in later versions of the library. Be sure to check the PyMySQL documentation and issue tracker for the latest information on this bug.