Pymongo.errors.serverselectiontimeouterror: py_ssize_t_clean macro must be defined for ‘#’ formats

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To better understand the issue you are facing, let’s break down the error message:

pymongo.errors.serverselectiontimeouterror: py_ssize_t_clean macro must be defined for ‘#’ formats

This error message is from the pymongo library and specifically indicates a ServerSelectionTimeoutError exception. This exception occurs when the MongoDB client is unable to connect to a MongoDB server within the specified time.

The second part of the error message, py_ssize_t_clean macro must be defined for '#' formats, provides some hints about the root cause.

From the error message, it seems like there is an issue with a formatting operation that requires the py_ssize_t_clean macro to be defined for the ‘#’ (hash) format. This suggests that the error is related to string formatting using the # format specifier.

To better understand this, let’s dive into an example:


import pymongo

def connect_to_mongodb():
    client = pymongo.MongoClient("mongodb://localhost:27017/")
    db = client["test"]
    collection = db["mycollection"]
    documents = collection.find()

    for document in documents:
        print(f"Document: {document}")

connect_to_mongodb()

In the above example, we are attempting to connect to a local MongoDB server running on the default port and then retrieve all documents from a collection. However, if the connection is not established within the specified timeout, a ServerSelectionTimeoutError will be raised, possibly with the added detail of py_ssize_t_clean macro must be defined for '#' formats.

To resolve this issue, you can follow these steps:

  1. Make sure that the MongoDB server is running and accessible from your code environment.
  2. Ensure that the connection string passed to MongoClient is correct. You can use the following connection string format: 
    
mongodb://[username:password@]host1[:port1][/[database][?options]]
  3. Check if there are any issues with the MongoDB server configuration or network connectivity.
  4. If you are using a replica set, verify that the replica set is properly configured and all members are running.
  5. Consider adjusting the timeout settings in your code. The default timeout is 30 seconds. You can increase it by passing the serverSelectionTimeoutMS option to the connection string or by setting the serverSelectionTimeoutMS property when creating the client object: 
    
client = pymongo.MongoClient("mongodb://localhost:27017/", serverSelectionTimeoutMS=5000)

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