The callable concept in Python includes a variety of different ways to create functions and objects that behave like functions. We can create callable objects that use memoization to maintain a cache of answers, therefore performing very quickly. In some cases, memoization is essential for creating an algorithm that finishes within a reasonable amount of time.
The concept of context allows us to create elegant, reliable resource management. The with statement defines a context and creates a context manager to control the resources used in that context. Python files are generally context managers; when used in a with statement, they are properly closed.
We'll look at several ways to create context managers using the tools in the contextlib module. Some other useful abstract base classes are in a separate submodule called collections.abc.
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