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Dunder Doc

by Valdir Stumm Jr

How I manage Virtualenvs with Pyenv

I have always been a happy virtualenvwrapper user, but I abandoned it last year to use pyenv and pyenv-virtualenv. I don’t really remember why, as virtualenvwrapper is awesome. The problem is that lately I haven’t been creating and managing a lot of virtualenvs, so I often find myself having to search through pyenv docs to do basic stuff when needed. That’s why I wrote down the usual steps that I follow so that next time I can remember (or find) more easily.

Black formats my code, and maybe it should format yours too

I’ve always been a bit skeptical about code formatters. I don’t know, I always felt like they would curb my freedom to format the code in my own way. Because, you know, no one formats code better than me. 😛 Joking aside, I got to know black about 2 years ago. Everyone was talking about it. A bunch of people adopted it. Massive codebases were being reformatted daily. It was the new kid on the block.

Handling Headers-Based Pagination on APIs with Python

The other day I was building a Python script to fetch some information about all my repositories on GitHub. Their API is pretty straightforward and well documented. Fetching my repos was as simple as: >>> import requests >>> response = requests.get("https://api.github.com/users/stummjr/repos") The thing is that such request gave me a list with all my repos on it. No info on pagination whatsoever on the response body. After a bit of research, I found out that GitHub APIs take advantage of the Link header to expose several pagination options.

CPython Optimizations

CPython is the reference implementation of the Python language. While there are several other implementations, CPython is by far the most popular one. These days, it comes bundled in most of the operating systems. Even though CPython is not the most performatic Python interpreter out there, it does some very interesting optimizations to speed itself and Python programs up. I am pretty curious about things like these and the rationale behind them, even though I know very little about it.

My Favorite IPython Tricks

It’s no secret that IPython is my favorite Python shell. I am the guy who is always asking everyone “did you try IPython already?” as soon as I see they opening the regular Python shell. Yes, I know, you’d probably hate me. The reason I like it so much is that IPython makes it very easy for me to incrementally experiment when coding. I consider experimentation to be a crucial step when writing software, as it helps to reduce the unkowns in a problem or technology.

Tips for boosting your Python scripts

I find myself writing quick command line scripts every so often. They usually automate a random task from my daily routine and end up saving me a bunch of time. These scripts usually start as quick and dirty snippets, but once I figure that they are not a one-off thing, then I iterate to make them more usable. There are several things that I find valuable in scripts like these:

Writing Scrapy Spiders in 2020

I am a huge fan of Scrapy and I’ve used it extensively for 3+ wonderful years working at Scrapinghub, the company behind this framework. It’s been one and a half year since I used it for the last time, but last week I had to build a spider for a personal project. To my surprise, I am not just rusty but pretty outdated in terms of the new shiny features of Scrapy.

Debugging Python with pudb

Pudb is, in my opinion, the most underrated Python package out there. I know this is a bold statement, but that’s how I feel about it. It helped me so much in a daily basis for so many years and I still feel like not too many people know about it. Debugging in Python There are several good debuggers for Python. I know a ton of people that use pdb, ipdb, VSCode/PyCharm embedded debuggers, among others.

Building a custom Flake8 plugin

Linters are everywhere. Be it in a fancy IDE, a CI pipeline or in the command line, linters help us to spot potential issues in our codebases. My favorite linter is flake8 and I use it in my VSCode setup, in my git pre-commit hooks and CI pipelines. But the thing is that flake8 doesn’t catch all the stuff I wanted it to catch. For example, I’d like my linter to catch the usage of the map and filter functions.

The curious case of the else in Python loops

One of the first things to stand out when I was starting with Python was the else clause. I guess everyone knows the normal usage of such clauses in any programming language, which is to define an alternate path for the if condition. Oddly enough, in Python we can add else clauses in loop constructions, such as for and while. For example, this is valid Python: for number in some_sequence: if is_the_magic_number(number): print('found the magic number') break else: print('magic number not found') Notice how the else is aligned with the for and not with the if.