--- title: Tiny Great Languages: Assembly | daily.dev description: A hands-on walkthrough of building a tiny two-pass assembler that targets the CPython VM's own bytecode instruction set. It covers disassembling Python... canonical: https://daily.dev/posts/tiny-great-languages-assembly-6tdaecfp3 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Tiny Great Languages: Assembly | daily.dev og:description: A hands-on walkthrough of building a tiny two-pass assembler that targets the CPython VM's own bytecode instruction set. It covers disassembling Python... og:url: https://daily.dev/posts/tiny-great-languages-assembly-6tdaecfp3 og:image: https://api.daily.dev/og/posts/6TDAECFP3.png og:image:alt: Tiny Great Languages: Assembly og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Tiny Great Languages: Assembly **[zserge's blog](https://daily.dev/sources/zserge)** · 7 min read · 0 upvotes · 0 comments ## Summary A hands-on walkthrough of building a tiny two-pass assembler that targets the CPython VM's own bytecode instruction set. It covers disassembling Python functions with the dis module, mapping opcodes like LOAD_CONST, LOAD_FAST, and BINARY_OP to their byte values, and implementing labels, constants, and jumps in under 50 lines of Python. A complete factorial program is assembled and run against the toy VM as a working example. This is part one of a series reimplementing classic 'Great Languages' (assembly, BASIC, Forth, Lisp, APL, PL/0) in minimal code. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do I find the byte values of CPython bytecode instructions like LOAD_CONST or BINARY_OP? Disassemble a Python function's compiled code with dis.dis() to see instruction names, then print factorial.__code__.co_code as hex to match numeric byte values to each opcode. For example, RESUME is 0x97, LOAD_FAST is 0x7c, LOAD_CONST is 0x64, COMPARE_OP is 0x6b, and RETURN_VALUE is 0x53 in a given CPython build. _daily.dev surfaces deep dives like this for developers exploring VM internals and bytecode._ ### What are the parameter values for BINARY_OP arithmetic operations in CPython bytecode? BINARY_OP is a meta-instruction whose parameter selects the arithmetic operation: addition is 0, subtraction is 10, multiplication is 5, and division is 3. It is also 4 bytes long instead of the usual 2, since the parameter is a 2-byte little-endian value followed by a zero byte. _Developers reverse-engineering VM bytecode can find similarly detailed breakdowns via daily.dev._ ### Why does building a custom assembler require two passes over the source code? A two-pass approach is needed because label addresses must be known before instructions referencing them can be assembled; the first pass records constants, variables, and label positions, while the second pass translates instructions into bytecode and resolves forward or backward label references into correct jump offsets. _daily.dev helps developers learning compiler and assembler design find hands-on writeups like this._ ## Similar posts on daily.dev - [A 1024 Byte Python Interpreter](https://daily.dev/posts/a-1024-byte-python-interpreter-ombsbouew) · Hackaday · 0 upvotes · 0 comments - [Micro language implementation: Calcium](https://daily.dev/posts/micro-language-implementation-calcium-7esmxmfk7) · Planet Python · 8 upvotes · 0 comments - [Making a Python interpreter in 1024 bytes](https://daily.dev/posts/making-a-python-interpreter-in-1024-bytes-vi1kzt7ex) · Lobsters · 0 upvotes · 0 comments - [Revisiting "Let's Build a Compiler"](https://daily.dev/posts/revisiting-let-s-build-a-compiler--usu6h8xiu) · Eli Bendersky · 0 upvotes · 0 comments - [Lil' Fun Langs](https://daily.dev/posts/lil-fun-langs-0ekzoi6my) · Hacker News · 0 upvotes · 0 comments --- Tags: [#python](https://daily.dev/tags/python), [#assembly](https://daily.dev/tags/assembly), [#cpython](https://daily.dev/tags/cpython) [View this post on daily.dev](https://daily.dev/posts/tiny-great-languages-assembly-6tdaecfp3) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Tiny Great Languages: Assembly","url":"https://daily.dev/posts/tiny-great-languages-assembly-6tdaecfp3","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/tiny-great-languages-assembly-6tdaecfp3"},"datePublished":"2026-08-23T10:20:14.948Z","dateModified":"2026-08-23T10:21:13.661Z","description":"A hands-on walkthrough of building a tiny two-pass assembler that targets the CPython VM's own bytecode instruction set. 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