Hello World!

I have been wanting to start a blog for a while… and it’s finally happening! In fact, I’m currently working on my first post about CPython string interning and I hope to publish it in a few days.

Meanwhile, I will leave you with two neat Python tricks I discovered last year in Raymond Hettinger’s PyCon talk: “Transforming Code into Beautiful, Idiomatic Python”.

The ignored context manager

Suppose you want to create a directory, but this directory might already exist:

import os

try:
    os.makedirs('/foo/bar')
except OSError:
    pass

Now, let’s define the ignored context manager as follows:

from contextlib import contextmanager

@contextmanager
def ignored(*exceptions):
    try:
        yield
    except exceptions:
        pass

Finally, this allows you to write:

import os

with ignored(OSError):
    os.makedirs('/foo/bar')

Nota bene: this is probably not the best example since you can handle this exception better by doing the following:

import errno
import os

try:
    os.makedirs('/foo/bar')
except OSError as e:
    if e.errno != errno.EEXIST:
        raise e

Still, I am sure you will find appropriate use cases for this context manager.

Read N bytes at a time from a buffer

This time, suppose you want to read 1024 bytes at a time from a file:

with open('/foo/bar/qux') as f:
    block = f.read(1024)
    
    while block:
        # do something with block
        block = f.read(1024)

Instead, Raymond suggests:

from functools import partial

with open('/foo/bar/qux') as f:
    for block in iter(partial(f.read, 1024), ''):
        # do something with block

I guess this can be extended to many other uses, be creative!