How can experienced developers often tell straight away which library may be helpful to solve a problem at hand?
Here’s a quick tip you can use to quickly find useful libraries included with the Python standard library:
The following two web pages contain one-sentence summaries of all modules available in the Python standard library. This makes for a great “cheat sheet” you can use for your research.
Python 3.x: https://docs.python.org/3/py-modindex.html
Python 2.7: https://docs.python.org/2/py-modindex.html
Experienced developers will have most of this memorized in some form or another, allowing them to quickly think of a built-in library that may help them because it relates to the problem at hand.
Now, should you memorize this list and learn it by heart? That might be challenging—ultimately what you want is having a bit of hands-on experience with as many modules as possible, not just rote memorization of one-sentence summaries.
But having this overview list as a summary you can search for keywords (use your browser’s built-in search functionality) is still immensely helpful. Be sure to bookmark it :)