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Optimization can be done through different metrics, such as, CPU performance (execution time) or memory footprint.

Optimizing your code makes sense when you are sure that the business logic in the code is correct and not going to change soon.

"First make it work. Then make it right. Then make it fast." ~ Kent Beck

Unless you're developing a performance-intensive product or a code dependency that is going to be used by other projects which might be performance-intensive, optimizing every aspect of the code can be overkill. For most of the scenarios, the 80-20 principle (80 percent of performance benefits may come from optimizing 20 percent of your code) will be more appropriate.

Most of the time we make intuitive guesses on what the bottlenecks are, but more often than not, our guesses are either wrong or just approximately correct. So, it's always advisable to use profiling tools to identify how often a resource is used and who is using the resource. For instance, a profiler designed for profiling execution time will measure how often and for how various long parts of the code are executed. Using a profiling mechanism becomes a necessity when the codebase grows large, and you still want to maintain efficiency.

Making Python command line fast

People like using software that feels fast, and Python programs tend to be slow to start running. What qualifies as fast is subjective, and varies by the type of tool and by the user's expectations.

Roughly speaking, for a command line program, people expect results almost instantaneously. For a tool that appears to be doing a simple task a sub-second result is enough, but under 200ms is even better.

Obviously to achieve this, your program actually has to be fast at doing its work. But what if you've written your code in Python, and it can take 800ms just to import your code, let alone start running it.

How fast can a Python program be?

TBC with the next sources

Minimize the relative import statements on command line tools

When developing a library, it's common to expose the main objects into the package under the variable __all__. The problem with command line programs is that each time you run the command it will load those objects, which can mean an increase of 0.5s or even a second for each command, which is unacceptable.

Following this string, if you manage to minimize the relative imports, you'll make your code faster.

Python's wiki discusses different places to locate your import statements. If you put them on the top, the imports that you don't need for that command in particular will worsen your load time, if you add them inside the functions, if you run the function more than once, the performance drops too, and it's a common etiquete to have all your imports on the top.

One step that you can do is to mark the imports required for type checking under a conditional:

from typing import TYPE_CHECKING

   from model import Object

This change can be negligible, and it will force you to use 'Object', instead of Object in the typing information, which is not nice, so it may not be worth it.

If you are still unable to make the loading time drop below an acceptable time, you can migrate to a server-client architecture, where all the logic is loaded by the backend (once as it's always running), and have a "silly" client that only does requests to the backend. Beware though, as you will add the network latency.

Don't dynamically install the package

If you install the package with pip install -e . you will see an increase on the load time of ~0.2s. It is useful to develop the package, but when you use it, do so from a virtualenv that installs it directly without the -e flag.


Last update: 2022-04-21