Python 3 min read

Python as your workbench

C++ becomes firmware on the chip; Python usually runs on your PC, next to the board. It is interpreted, so there is no build step between a question and its answer. That makes it the ideal bench tool: a calculator that speaks hex, a log reader and a test runner in one.

Left, compiled C++: main.cpp is translated once by a compiler into firmware.bin, which the MCU runs. Right, interpreted Python: the python interpreter reads script.py and runs each statement in turn, so the output appears straight away; you can also type statements into the REPL. — C++ is translated once and flashed; Python runs each statement as it reads it.

Compiled vs interpreted

A compiler translates your whole program into machine code before it runs: that is how C++ becomes firmware.bin. An interpreter reads the program and runs it statement by statement. Python is interpreted, so you can change a line and run it again straight away. You give up raw speed, but on the bench the slow part is you, not the CPU.

The REPL: a calculator that speaks hex

Type python in a terminal with no file name and you get the >>> prompt. This is the REPL: it reads a line, evaluates it, prints the result and loops. It is the fastest way to check a baud-rate divider or decode a register value. The same lines also work in a script, where you call print() to see results:

first.pyPython

# The REPL prints each result itself; a script prints what you ask for.print(0x2A + 1)print(hex(255), bin(5))print(72_000_000 // 115_200)  # UART divider for 115200 baud at 72 MHz

Output

43
0xff 0b101
625

Your first script

Save the lines in a file ending in .py and run python first.py. Lines starting with # are comments. Words such as if, for, def and class are keywords, so you can't use them as names. Any editor works; the python.org installer also includes a simple one called IDLE.