Troubleshooting “wrong-type-argument markerp nil” Error in Python Shell-mode PDB Tracking

What will you learn?

In this comprehensive guide, you will delve into the intricacies of resolving the perplexing error message “wrong-type-argument markerp nil” that often surfaces during shell-mode PDB tracking in Python. By understanding the root cause and implementing effective solutions, you will master the art of troubleshooting such errors with confidence.

Introduction to the Problem and Solution

Encountering the cryptic error “wrong-type-argument markerp nil” while engaging in shell-mode PDB tracking within Python signifies a mismatch in how a function or method is being utilized. To conquer this challenge, meticulous scrutiny of the code snippet triggering the error is imperative to ensure correct argument usage.

One prevalent scenario where this error manifests is when setting breakpoints or monitoring code execution using PDB (Python Debugger) within a shell environment. By deciphering the operational mechanics of PDB and pinpointing the source of incorrect argument types, you can adeptly troubleshoot and rectify this issue.


# Utilizing PDB for debugging purposes
import pdb

# Set breakpoints at desired locations

# Your code here

# Exit debugger mode post debugging completion

# Copyright PHD

# Explore further resources at


When leveraging Python’s PDB module for debugging tasks, employing pdb.set_trace() at strategic junctures in your code facilitates pausing execution for variable inspection. The “wrong-type-argument markerp nil” error commonly arises due to improper utilization of PDB functions or incorrect argument passing.

To sidestep encountering this error: 1. Validate Arguments: Ensure accurate argument provision while setting breakpoints or utilizing other PDB features. 2. Debugging Proficiency: Grasp the functionality of PBD within a shell context and seamlessly integrate it into your workflow. 3. Error Mitigation: Implement robust exception handling mechanisms if necessary during debugging endeavors.

  1. How can one prevent encountering the “wrong-type-argument markerp nil” error?

  2. The key lies in correctly utilizing PBD functions by supplying appropriate arguments as per their intended usage.

  3. What impact does shell mode have on triggering this error?

  4. The choice of shell mode for running your Python application influences how PBD interacts with your code; misconfigurations can lead to such errors.

  5. Can external packages conflict with PBD, resulting in this error?

  6. Indeed, clashes between third-party libraries and debugger configurations may give rise to unexpected errors like “wrong-type-argument markerp nil”.

  7. Is there a disparity between direct script execution versus debugger-assisted runs concerning this issue?

  8. Running scripts directly might not always trigger such errors as they typically surface during interactive debugging sessions facilitated by tools like PBD.

  9. Should one restart their kernel/console if confronted with this error while using Jupyter notebooks?

  10. Restarting could potentially resolve transient glitches causing the mentioned error; however, comprehending its origin is crucial for long-term prevention.


In conclusion, mastering the resolution of errors like “wrong-type-argument markerp nil” demands precision when navigating environments necessitating interactive debugging support from tools like PDB. By adhering to best practices elucidated above and honing proficiency in troubleshooting strategies, developers can elevate their coding prowess while minimizing disruptions stemming from technical obstacles.

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