Python

Python language features, pandas and scikit-learn recipes, and the errors that trip people up.

33 articles

• Fix TypeError: datetime Is Not JSON Serializable

  Fix Python datetime JSON serialization errors with ISO 8601, timezone-safe encoders, Flask, Django, FastAPI, pandas, debugging, tests, and prevention.

  July 27, 2026

• Fix AttributeError: 'DataFrame' object has no attribute 'append'

  Pandas 2.0 removed DataFrame.append(). Replace it with pd.concat — and if you were appending in a loop, collect rows in a list and build the DataFrame once.

  July 25, 2026

• Fix ImportError: cannot import name 'Mapping' from 'collections'

  Python 3.10 removed the old collections.Mapping alias. Import from collections.abc instead — but it's usually an old dependency, so read the traceback and upgrade it.

  July 25, 2026

• Fix ModuleNotFoundError: No module named 'cv2' (OpenCV)

  You import cv2 but the pip package is opencv-python — and there are four variants. Pick the right one, and preempt the libGL.so.1 error on servers with headless.

  July 25, 2026

• Fix ModuleNotFoundError: No module named 'dotenv'

  The package is python-dotenv but the import is dotenv — and pip install dotenv is the wrong package. Install python-dotenv into the interpreter you actually run.

  July 25, 2026

• Fix ValueError: too many values to unpack (expected 2)

  This means the left side has fewer targets than the right side has values. Count both sides, iterate dicts with .items(), and use star-unpacking for extras.

  July 25, 2026

• Fix CUDA and cuDNN Library Load Errors in TensorFlow: A Diagnostic Guide

  Every TensorFlow CUDA library error — libcublas, libcudart, libnvinfer, cuDNN — traced to one of four root causes, with the order to diagnose them.

  July 21, 2026

• Common Pandas Errors and Gotchas: A Diagnostic Guide

  The pandas errors that waste the most time — SettingWithCopyWarning, Int64Index errors, silent assignment failures, and merge row explosions — and their causes.

  July 21, 2026

• Fix IDE Auto-Completion Failure for tensorflow.keras

  Autocomplete fails for tf.keras because it's a lazily-loaded alias that static analyzers can't follow. Your code still runs — import from keras directly to give the IDE a real module to introspect.

  June 8, 2023

• Fix ImportError: cannot import name 'abs'

  This ImportError comes from a shadowed or half-installed package (classically TensorFlow) or a circular import — not from the abs builtin. Here's how to find which one and fix it.

  June 8, 2023

• How to convert a date to Unix epoch time in Python?

  Convert a date to Unix epoch time in Python with dt.timestamp(). Handle timezones correctly so a naive datetime isn't misread as local time.

  January 11, 2023

• Fix TypeError: Can Only Concatenate str (Not "NoneType") to str

  Fix Python's str and NoneType concatenation error by finding the None value, repairing missing returns, choosing safe defaults, and avoiding common bad fixes.

  January 10, 2023

• How Inheritance Works in Python: super(), the MRO & Composition vs Inheritance

  Python inheritance for interviews: single and multiple inheritance, super() and cooperative __init__, the method resolution order (MRO / C3 linearisation) and the diamond problem, mixins, abstract base classes, and when to favour composition over inheritance.

  January 9, 2023

• Object-Oriented Programming in Python: Classes, Objects & the Four Pillars (Interview Guide)

  A senior-level tour of Python OOP for interviews: classes and objects, __init__ and self, instance vs class vs static methods, @property, dunder methods, @dataclass, and the four pillars — encapsulation, abstraction, inheritance, and polymorphism.

  January 9, 2023

• Polymorphism in Python: Duck Typing, Dunder Methods & singledispatch (Interview Guide)

  How polymorphism really works in Python — duck typing (no shared base class needed), method overriding, operator overloading via dunder methods, functools.singledispatch, and Protocols — with the interview traps around Python's lack of method overloading.

  January 8, 2023

• OOPS Concept In Python interview questions

  OOPS, or Object-Oriented Programming Systems, is a programming paradigm that is based on the concept of objects, which have properties and methods.

  January 7, 2023

• Seaborn for Data Visualization in Python

  Seaborn is a statistical plotting library on top of matplotlib. It works with pandas DataFrames and offers concise, attractive charts. Getting started.

  January 5, 2023

• How to Fix AttributeError: 'Int64Index' object has no attribute 'month'

  This pandas error means you called a datetime accessor like .month on an integer index. Convert the index to datetimes first — and know that Int64Index itself was removed in pandas 2.0.

  January 3, 2023

• How to Append Multiple Excel Files together in python?

  Append multiple Excel files in Python: read each with pandas, collect them in a list, then pd.concat once. Why concatenating in the loop is slow.

  January 2, 2023

• How to Fix Error 524 While Running JupyterLab on Google Cloud Platform

  HTTP 524 is a Cloudflare timeout, not a Jupyter error — the origin took longer than 100 seconds to respond. Fix it by not blocking on long cells, or by bypassing the proxy with an SSH tunnel.

  January 2, 2023

• Pandas: drop vs Boolean Filtering vs df.filter() — What Each One Actually Does

  drop removes rows/columns by LABEL; boolean masking (df[df.a > 2]) keeps rows by CONDITION; df.filter() selects LABELS by name/regex — it does NOT take a boolean mask. Worked examples of each.

  December 27, 2022

• How to implement custom loss function in scikit-learn?

  To implement a custom loss function in scikit-learn, we'll need to use the make_scorer function

  December 25, 2022

• How to use XGBoost in Python?

  Use XGBoost in Python via its scikit-learn API (XGBClassifier/Regressor) or native DMatrix API. Key hyperparameters and early stopping explained.

  December 24, 2022

• transform vs fit_transform in scikit-learn: The Data-Leakage Rule (and Why You Should Use a Pipeline)

  fit vs transform vs fit_transform in scikit-learn, and the rule that prevents data leakage: fit on train only, transform train and test with the training parameters. Plus why a Pipeline is the correct way to enforce this.

  December 21, 2022

• Difference between StratifiedKFold and StratifiedShuffleSplit in sklearn

  StratifiedKFold makes k non-overlapping folds (every sample tested once); StratifiedShuffleSplit draws independent random splits. When to use each.

  December 20, 2022

• Plot Multiple Columns from a Pandas DataFrame (Shared Axes, Subplots, Dual Axis)

  Plot several DataFrame columns at once: pass a LIST to y (df.plot(y=['a','b'])), use x for a single shared axis, subplots=True for separate panels, and secondary_y for a dual axis.

  December 19, 2022

• Collapse Repeated Rows into One per Key in Pandas (groupby + agg)

  Reduce repeated rows to a single row per key with groupby().agg(): sum/mean/first per column, collect repeated values into a list with agg(list), or reshape with pivot_table.

  December 18, 2022

• Getting started with PyTorch

  Get started with PyTorch: install it, create GPU-accelerated tensors, build a model with nn.Module, and train with autograd. A beginner's tutorial.

  December 17, 2022

• How to fix Python ImportError: lxml not found, please install it

  Python: ImportError: lxml not found, please install it

  October 20, 2022

• Fix AttributeError: module 'pexpect' has no attribute 'TIMEOUT'

  AttributeError: module 'pexpect' has no attribute 'TIMEOUT' means a stale module is loaded or a local file shadows the package. How to tell which, and fix it.

  October 20, 2022

• How to fix SettingWithCopyWarning in Pandas?

  SettingWithCopyWarning means pandas can't tell if you're modifying a view or a copy, so your assignment may silently do nothing. The view-vs-copy .loc fix.

  October 16, 2022

• Fix “Max Retries Exceeded with URL” in Python Requests

  Fix Python Requests Max retries exceeded errors by identifying DNS, refused connection, timeout, TLS, proxy, or HTTP-status causes before adding retries.

  October 14, 2022

• How to use ternary conditional operator in Python?

  Python's ternary is a conditional expression: value_if_true if condition else value_if_false — not C-style condition ? a : b. Syntax, examples, and limits.

  October 14, 2022

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