Loop & Branch: practical Python and web development tutorials

Tested answers for everyday code.

Short, tested answers to the questions developers actually search for: how to split a string, why pandas cannot decode a CSV, what NoneType object is not subscriptable means, how to send a request with urllib3.

Every tutorial is written for this site, runs on current versions of the libraries it covers, and links to the official documentation for the details.

Python tutorialsData with pandas & NumPy

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Scrapy vs Selenium: choosing a Python web scraping tool

Architecture, JavaScript rendering, speed, scaling and pipelines compared, with working code for each and a note on when scrapy-playwright is the better middle ground.

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The six questions readers bring most often.

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Split a string into a list

Split strings into lists in Python: str.split with and without sep, maxsplit, rsplit, splitlines, re.split for multiple delimiters, list(), csv and shlex.

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'NoneType' object is not subscriptable

Fix 'NoneType' object is not subscriptable: common causes (list.sort(), dict.get, re.match, JSON null), reading the traceback, and catching it with mypy.

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UnicodeDecodeError in read_csv

Why pd.read_csv raises UnicodeDecodeError: 'utf-8' codec can't decode byte, and how to fix it with the right encoding, BOM handling and UTF-8 conversion.

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HTTP requests with urllib3

How to send GET and POST requests with urllib3: PoolManager, query fields, JSON bodies, headers, timeouts, Retry, redirects, TLS, streaming and errors (v2).

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Nested dictionary values

Get values from nested dictionaries in Python: chained indexing, safe .get() chains, a deep_get helper, lists in dicts, recursion, json_normalize and glom.

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Install packages in PyCharm

Install Python packages in PyCharm via the Packages tool window, interpreter settings or pip; venv vs conda, requirements.txt and fixing import errors.

Browse by section

Every tutorial on the site, grouped the way you would look for it.

python/ 10 tutorials

Core language: strings, lists, dictionaries, numbers and the errors you meet along the way.

tools/ 6 tutorials

Interpreters, packages, notebooks, IDEs and file conversion.

web/ 5 tutorials

Back-end and front-end building blocks: CRUD, calendars, e-commerce settings, scraping.

data/ 4 tutorials

NumPy, pandas and statistics: reading files, formatting numbers, describing distributions.