Background
Why replace Tcl with Python?
Many VLSI and EDA tools expose their functionality through a custom Tcl interpreter. As automation scripts for these tools grow in complexity, Tcl’s limited abstraction and encapsulation mechanisms make them increasingly difficult to maintain.
NoTcl allows these tools to be scripted in Python instead, which offers several practical advantages:
Better language support for complex automation. Python’s module system, exception handling, and standard library make it easier to write, test, and maintain large automation scripts.
Tcl-based tools become Python libraries. NoTcl wraps each tool in a Python interface, allowing tool functionality to be imported and used like any other Python library, integrated into larger Python applications.
Tool-independent Python interpreter across tools. Different EDA tools embed different Tcl versions with varying feature sets. Shared Tcl code between tools often requires version-specific workarounds. With NoTcl, all tool-specific logic is expressed in Python, eliminating Tcl version compatibility issues.
Straightforward data sharing between tools. When multiple tools are invoked sequentially from the same Python process, intermediate results can be passed between them using ordinary Python data structures.
How NoTcl differs from other approaches
Several other projects bridge Tcl and Python (see Accessing Tcl and Python from one another in the Tcl wiki). NoTcl differs from these in two key ways:
No C extensions required. The Tcl tool executes only a small, pure-Tcl communication script. There is no need to compile or load a shared library into the tool’s Tcl interpreter, which makes NoTcl compatible with tools that do not support loading custom C extensions.
Opaque handle preservation. References to all Tcl command return values are kept in a Tcl array, allowing opaque handles (pointers to internal data structures) to be held in Python and passed back to Tcl without losing their internal representation. This matters for tools that distinguish handles from their string representations.
Related projects: