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001 Ai Topological Sort

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TLDR: Constant Folding in Python

Date: 2021-01-10 Source: https://arpitbhayani.me/blogs/constant-folding-python

Overview

Explore Python's constant folding - how it optimizes code by evaluating expressions at compile time. Dive into CPython's elegant implementation. Python tries to fold every single constant expression present but there are some cases where even though the expression is constant, but Python chooses not to fold it.

Key Points

  • Scope of Constant Folding: Python tries to fold every single constant expression present but there are some cases where even though the expression is constant, but Python chooses not to fold it.
  • Every programming language aims to be performant in its niche and achieving superior performance requires a lot of compiler level optimizations.
  • One famous optimization technique is Constant Folding where during compile time the engine tries to recognize constant expressions, evaluate them, and replaces the expression with this newly evaluated value, making the runtime leaner.
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  • In this essay, we dive deep and find what exactly is Constant Folding, understand the scope of it in the world of Python and finally go through Python’s source code - CPython - and find out how elegantly Python actually implements it.
  • In Constant Folding, the engine finds and evaluates constant expressions at compile time rather than computing them at runtime, making the runtime leaner and faster.
  • When the compiler encounters a constant expression, like above, it evaluates the expression and replaces it with the evaluated value.

    • Takeaway

    Python tries to fold every single constant expression present but there are some cases where even though the expression is constant, but Python chooses not to fold it.