rixx.de (Posts about studying)

December 13: Python Concurrent Execution Modules

rixx — Sat, 19 Dec 2020 07:00:00 GMT

Now we get to talk about a completely trivial topic, barely worth mentioning: Concurrent execution, including threading, multiprocessing, concurrent, subprocess, sched and queue.

Now, you might say, "wait a second, it is not December 13th!", and … you would be right. Life got in the way and I had to spend a week figuring some things out, and pushing out a blog post about concurrency in Python did not quite fit in with that. Now all the things are figured out, and I'm continuing the Traversal of the Python Standard Library Documentation.

Highlights

Oh god Popen has so many arguments.
Python ships a "general purpose event scheduler"

December 12: Context Variables

rixx — Sat, 12 Dec 2020 07:00:00 GMT

As part of the Python Standard Library documentation traversal, we're following up on yesterday's exhausting post about Operating System Services with probably the shortest chapter yet: the contextvars module. It's not cheating, it really is listed as its own high-level documentation section!

December 11: Python Operating System Services

rixx — Fri, 11 Dec 2020 07:00:00 GMT

After some restful days, today's Python Standard Library Traversal follows up yesterday's Cryptographic Service Modules with all the generic OS interaction modules. That is os (but not os.path, we did that a week ago), io, time, argparse, getopt, logging and its submodules, getpass, curses and submodules, platform, errno and ctypes. Strap in!

Highlights

On Windows, os.startfile() acts like double-clicking the file.
There are way too many ways to start new processes in Python.
"seconds since epoch" usually excludes leap seconds.
argparse is honestly not as bad as I remembered it. Stockholm syndrome?
logger.getChild() is like calling getLogger() on the full target name, very useful when you use stand-in values like __name__.
logger.handlers.TimedRotatingFileHandler and logger.handlers.RotatingFileHandler handle log file rotation, nice!
logger.handlers.HTTPHandler defaults to secure=False.
You can change the default %-style string formatting in logging formatters to str.format() or string.Template.
You can query the platform you are running on with the platform module.

December 10: Python Cryptographic Service Modules

rixx — Thu, 10 Dec 2020 07:00:00 GMT

Shhh! 🤫 As part of the Python Standard Library traversal, after yesterday's look at file format modules, today is going to be all about secrets. Well, all about secrets and hmac and hashlib, to be precise.

Highlights

There's an awful lot of hash algorithms in hashlib.
The secrets module exists and is suitable for (reasonably) strong randomness, eg for generating long secret URLs.

December 9: Python File Format Modules

rixx — Wed, 09 Dec 2020 07:00:00 GMT

Combining the commonplace and the weirdly specific: As part of the Python Standard Library traversal, after yesterday's short post about data compression and archiving modules, today we're going to look at Python file format modules. Those include csv, configparser, netrc, xdrlib and the forgettable plistlib.

Highlights

Writing your own csv dialect is extremely easy. I wonder how cursed you can make it.
configparser has an extended interpolation mode that allows you to refer to values from other sections like %{OtherSection:other_value}
You can configure lots of things about configparser, like the delimiters, comment prefix, strict mode, enable multiline strings with empty lines, permit empty/flag values, …
Why on earth is csv in a different documentation block from json and xml?
I learnt that the netrc FTP configuration format exists, and requires its own stdlib support module.
I learnt that xdr file format exists, and at least the Python interface sounds pretty annoying.
I learnt that plist Apple format exists, and it sounds not that bad.

December 8: Pyton Data Compression and Archiving Modules

rixx — Tue, 08 Dec 2020 07:00:00 GMT

As part of the Python Standard Library traversal, after yesterday's short post about data persistence, today we're going to look at Python data compression modules. There are not too many of them, but definitely more than I knew: zlib, gzip, bz2, lzma, zipfile, tarfile.

Highlights

Now I know that Python supports six different main compression protocols out of the box.
The zipfile module has a CLI interface for compression, extraction and listing of archives.
Same for tarfile.
When opening a tarfile, you can pass the intended compression algorithm with the file mode, like w:bz2.

December 7: Python Data Persistence Modules

rixx — Mon, 07 Dec 2020 07:00:00 GMT

Strap in, this is a long one: As part of the Python Standard Library traversal, after yesterday's short post about binary data services, today we're going to look at Python data type modules. There's a lot of them: datetime, calendar, collections, heapq, bisect, array, weakref, types, copy, pprint, reprlib and enum.

Highlights

You can use shelve to store pickled objects in a persistent key-value store.
The Unix dbm library is a thing that exists and has Python standard library support.

December 6: Python File and Directory Access

rixx — Sun, 06 Dec 2020 07:00:00 GMT

There's no place where "one obvious way to do things" fails as much as it does with file and OS interaction. As part of the Python Standard Library traversal, after yesterday's post about functional programming modules, today we're going to look at the file and directory access modules. Yes, all of them: pathlib, os.path, fileinput, stat, filecmp, tempfile, glob, fnmatch, linecache and shutil.

Highlights

The 80% overlap between pathlib and os.path is bordering on hilarious. One obvious way indeed.
fileinput is really weird.
stat allows you to query and extract results of os.stat()
shutil.diskusage() returns total, used and free bytes for a given directory.
shutil.which() looks up executables (platform independent which)
shutil.make_archive supports zip, tar, gztar, bztar and xtar out of the box.

December 5: Python Functional Programming Modules

rixx — Sat, 05 Dec 2020 11:00:00 GMT

A short entry for a change: As part of the Python Standard Library traversal, after yesterday's short post about Python's numeric and mathematical modules, I'm taking a look at itertools, functools and operator.

Highlights

There really are a lot of itertools functions.
functools contains a cached_property decorator.
I finally know what lru_cache does.
Apparently Python has a type of function overloading, by type of first argument, with singledispatch.
There are operator functions for performing in-place operations like +=.
operator.attrgetter can retrieve multiple and nested attributes.
operator.itemgetter can retrieve multiple items.

December 4: Python Numeric and Mathematical Modules

rixx — Fri, 04 Dec 2020 07:00:00 GMT

Today is a bit less bad than yesterday: As part of the Python Standard Library traversal, after yesterday's extensive post about data types, today we're going to look at Python modules that take care of numbers and maths and make us very happy because we don't need to implement them ourselves. Or wait for NumPy to install.

Highlights

The numbers module contains abstract base classes so you can check for features of given numbers using isinstance.
The Python documentation takes a stand for tau and against pi. Good documentation.
cmath provides mathematical operations and functions for complex numbers – it exists separately from math so that people aren't surprised when they run math.sqrt(-1). 🤣
fractions.limit_denominator() allows you to take a float and turn it into the number it was meant to be. Go team fractions.
The fact that decimal is singular and fractions is plural will never cease to confuse me.
Apparently there's both random.gauss() and random.normalvariate() ???
statistics.NormalDist creates a normal distribution either from a set of samples or the mean and a standard deviation.